The Allies or the Entente (, ) was an international military
coalition
A coalition is formed when two or more people or groups temporarily work together to achieve a common goal. The term is most frequently used to denote a formation of power in political, military, or economic spaces.
Formation
According to ''A G ...
of countries led by the
French Republic
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
, the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
, the
Russian Empire
The Russian Empire was an empire that spanned most of northern Eurasia from its establishment in November 1721 until the proclamation of the Russian Republic in September 1917. At its height in the late 19th century, it covered about , roughl ...
, the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, the
Kingdom of Italy
The Kingdom of Italy (, ) was a unitary state that existed from 17 March 1861, when Victor Emmanuel II of Kingdom of Sardinia, Sardinia was proclamation of the Kingdom of Italy, proclaimed King of Italy, until 10 June 1946, when the monarchy wa ...
, and the
Empire of Japan
The Empire of Japan, also known as the Japanese Empire or Imperial Japan, was the Japanese nation state that existed from the Meiji Restoration on January 3, 1868, until the Constitution of Japan took effect on May 3, 1947. From Japan–Kor ...
against the
Central Powers
The Central Powers, also known as the Central Empires,; ; , ; were one of the two main coalitions that fought in World War I (1914–1918). It consisted of the German Empire, Austria-Hungary, the Ottoman Empire, and the Kingdom of Bulga ...
of the
German Empire
The German Empire (),; ; World Book, Inc. ''The World Book dictionary, Volume 1''. World Book, Inc., 2003. p. 572. States that Deutsches Reich translates as "German Realm" and was a former official name of Germany. also referred to as Imperia ...
,
Austria-Hungary
Austria-Hungary, also referred to as the Austro-Hungarian Empire, the Dual Monarchy or the Habsburg Monarchy, was a multi-national constitutional monarchy in Central Europe#Before World War I, Central Europe between 1867 and 1918. A military ...
, the
Ottoman Empire
The Ottoman Empire (), also called the Turkish Empire, was an empire, imperial realm that controlled much of Southeast Europe, West Asia, and North Africa from the 14th to early 20th centuries; it also controlled parts of southeastern Centr ...
, and the
Kingdom of Bulgaria
The Tsardom of Bulgaria (), also known as the Third Bulgarian Tsardom (), usually known in English as the Kingdom of Bulgaria, or simply Bulgaria, was a constitutional monarchy in Southeastern Europe, which was established on , when the Bulgaria ...
in
World War I
World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
(1914–1918).
By the end of the first decade of the 20th century, the major European powers were divided between the
Triple Entente and the
Triple Alliance. The Triple Entente was made up of the United Kingdom, France, and Russia. The Triple Alliance was originally composed of Germany, Austria–Hungary, and Italy, but Italy remained neutral in 1914. As the war progressed, each coalition added new members. Japan joined the Entente in 1914 and, despite proclaiming its neutrality at the beginning of the war, Italy also joined the Entente in 1915. The term "Allies" became more widely used than "Entente", although the United Kingdom, France, Russia, and Italy were also referred to as the Quadruple Entente and, together with Japan, as the Quintuple Entente. The five
British Dominions (
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
,
Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
,
New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
,
Newfoundland
Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the population ...
, and the
Union of South Africa
The Union of South Africa (; , ) was the historical predecessor to the present-day South Africa, Republic of South Africa. It came into existence on 31 May 1910 with the unification of the British Cape Colony, Cape, Colony of Natal, Natal, Tra ...
) all fought alongside the British. The colonies of Allied countries, such as the
American Philippines,
Belgian Congo
The Belgian Congo (, ; ) was a Belgian colonial empire, Belgian colony in Central Africa from 1908 until independence in 1960 and became the Republic of the Congo (Léopoldville). The former colony adopted its present name, the Democratic Repu ...
,
British India
The provinces of India, earlier presidencies of British India and still earlier, presidency towns, were the administrative divisions of British governance in South Asia. Collectively, they have been called British India. In one form or another ...
,
French Algeria
French Algeria ( until 1839, then afterwards; unofficially ; ), also known as Colonial Algeria, was the period of History of Algeria, Algerian history when the country was a colony and later an integral part of France. French rule lasted until ...
, and
Japanese Korea, were also used as a source of manpower by the colonial powers.
The United States joined near the end of the war in 1917 (the same year in which Russia withdrew from the conflict) as an "associated power" rather than an official ally. Primary reasons for why the United States joined the war include the unrestricted submarine warfare waged by Germany in the Atlantic, the revelation of the
Zimmermann telegram, and strong economic and political ties with the Allies. Other "associated members" of the Allies included
Serbia
, image_flag = Flag of Serbia.svg
, national_motto =
, image_coat = Coat of arms of Serbia.svg
, national_anthem = ()
, image_map =
, map_caption = Location of Serbia (gree ...
,
Belgium
Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...
,
Montenegro
, image_flag = Flag of Montenegro.svg
, image_coat = Coat of arms of Montenegro.svg
, coa_size = 80
, national_motto =
, national_anthem = ()
, image_map = Europe-Mont ...
,
Asir,
Nejd and Hasa,
Portugal
Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...
,
Romania
Romania is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to ...
,
Hejaz
Hejaz is a Historical region, historical region of the Arabian Peninsula that includes the majority of the western region of Saudi Arabia, covering the cities of Mecca, Medina, Jeddah, Tabuk, Saudi Arabia, Tabuk, Yanbu, Taif and Al Bahah, Al-B ...
,
Panama
Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...
,
Cuba
Cuba, officially the Republic of Cuba, is an island country, comprising the island of Cuba (largest island), Isla de la Juventud, and List of islands of Cuba, 4,195 islands, islets and cays surrounding the main island. It is located where the ...
,
Greece
Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...
,
China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
,
Siam,
Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
,
Armenia
Armenia, officially the Republic of Armenia, is a landlocked country in the Armenian Highlands of West Asia. It is a part of the Caucasus region and is bordered by Turkey to the west, Georgia (country), Georgia to the north and Azerbaijan to ...
,
Luxembourg
Luxembourg, officially the Grand Duchy of Luxembourg, is a landlocked country in Western Europe. It is bordered by Belgium to the west and north, Germany to the east, and France on the south. Its capital and most populous city, Luxembour ...
,
Guatemala
Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...
,
Nicaragua
Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...
,
Costa Rica
Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...
,
Haiti
Haiti, officially the Republic of Haiti, is a country on the island of Hispaniola in the Caribbean Sea, east of Cuba and Jamaica, and south of the Bahamas. It occupies the western three-eighths of the island, which it shares with the Dominican ...
,
Liberia
Liberia, officially the Republic of Liberia, is a country on the West African coast. It is bordered by Sierra Leone to Liberia–Sierra Leone border, its northwest, Guinea to Guinea–Liberia border, its north, Ivory Coast to Ivory Coast–Lib ...
, and
Honduras
Honduras, officially the Republic of Honduras, is a country in Central America. It is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean at the Gulf of Fonseca, ...
. The treaties signed at the
Paris Peace Conference recognized the British Empire, France, Italy, Japan, and the United States as "the Principal Allied and Associated Powers"; France, the UK, Italy, and the US were also referred as the "
Big Four" top powers of the war.
Background
When the war began in 1914, the
Central Powers
The Central Powers, also known as the Central Empires,; ; , ; were one of the two main coalitions that fought in World War I (1914–1918). It consisted of the German Empire, Austria-Hungary, the Ottoman Empire, and the Kingdom of Bulga ...
were opposed by the
Triple Entente, formed in 1907 when the agreement between the United Kingdom and
Russia
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
complemented existing agreements between the three powers.
Fighting commenced when Austria invaded
Serbia
, image_flag = Flag of Serbia.svg
, national_motto =
, image_coat = Coat of arms of Serbia.svg
, national_anthem = ()
, image_map =
, map_caption = Location of Serbia (gree ...
on 28 July 1914, in response to the
assassination of Archduke Franz Ferdinand
The assassination of Archduke Franz Ferdinand was one of the key events that led to World War I. Archduke Franz Ferdinand of Austria, heir presumptive to the Austria-Hungary, Austro-Hungarian throne, and his wife, Sophie, Duchess of Hohenberg ...
, heir to Emperor
Franz Joseph I; this brought Serbia's ally
Montenegro
, image_flag = Flag of Montenegro.svg
, image_coat = Coat of arms of Montenegro.svg
, coa_size = 80
, national_motto =
, national_anthem = ()
, image_map = Europe-Mont ...
into the war on 9 August and it attacked the Austrian naval base at
Cattaro, modern Kotor. At the same time, German troops carried out the
Schlieffen Plan, entering neutral
Belgium
Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...
and
Luxembourg
Luxembourg, officially the Grand Duchy of Luxembourg, is a landlocked country in Western Europe. It is bordered by Belgium to the west and north, Germany to the east, and France on the south. Its capital and most populous city, Luxembour ...
; over 95% of Belgium was occupied but the Belgian Army held their lines on the
Yser Front throughout the war. This allowed Belgium to be treated as an Ally, in contrast to Luxembourg which retained control over domestic affairs but was
occupied by the German military.
In the East, between 7 and 9 August the Russians entered German
East Prussia
East Prussia was a Provinces of Prussia, province of the Kingdom of Prussia from 1772 to 1829 and again from 1878 (with the Kingdom itself being part of the German Empire from 1871); following World War I it formed part of the Weimar Republic's ...
and Austrian
Eastern Galicia
Eastern Galicia (; ; ) is a geographical region in Western Ukraine (present day oblasts of Lviv Oblast, Lviv, Ivano-Frankivsk Oblast, Ivano-Frankivsk and Ternopil Oblast, Ternopil), having also essential historic importance in Poland.
Galicia ( ...
.
Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
joined the Entente by declaring war on Germany on 23 August, then Austria on 25 August. On 2 September, Japanese forces surrounded the German
Treaty Port of
Tsingtao (now Qingdao) in China and occupied German colonies in the Pacific, including the
Mariana,
Caroline, and
Marshall Islands
The Marshall Islands, officially the Republic of the Marshall Islands, is an island country west of the International Date Line and north of the equator in the Micronesia region of the Northwestern Pacific Ocean.
The territory consists of 29 c ...
.
Despite its membership of the
Triple Alliance,
Italy
Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
remained neutral until 23 May 1915 when it joined the Entente, declaring war on Austria but not Germany. On 17 January 1916,
Montenegro
, image_flag = Flag of Montenegro.svg
, image_coat = Coat of arms of Montenegro.svg
, coa_size = 80
, national_motto =
, national_anthem = ()
, image_map = Europe-Mont ...
capitulated and left the Entente; this was offset when Germany declared war on
Portugal
Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...
in March 1916, while
Romania
Romania is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to ...
commenced hostilities against Austria on 27 August.
On 6 April 1917, the United States entered the war as a co-belligerent, along with the associated allies of
Liberia
Liberia, officially the Republic of Liberia, is a country on the West African coast. It is bordered by Sierra Leone to Liberia–Sierra Leone border, its northwest, Guinea to Guinea–Liberia border, its north, Ivory Coast to Ivory Coast–Lib ...
,
Siam and
Greece
Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...
. After the 1917
October Revolution
The October Revolution, also known as the Great October Socialist Revolution (in Historiography in the Soviet Union, Soviet historiography), October coup, Bolshevik coup, or Bolshevik revolution, was the second of Russian Revolution, two r ...
, Russia left the Entente and agreed to a separate peace with the Central Powers with the signing of the
Treaty of Brest-Litovsk on 3 March 1918. Romania was forced to do the same in the May 1918
Treaty of Bucharest but on 10 November, it repudiated the Treaty and once more declared war on the Central Powers.
These changes meant the Allies who negotiated the
Treaty of Versailles
The Treaty of Versailles was a peace treaty signed on 28 June 1919. As the most important treaty of World War I, it ended the state of war between Germany and most of the Allies of World War I, Allied Powers. It was signed in the Palace ...
in 1919 included the United Kingdom, France, Italy, Japan and the United States; Part One of the Treaty agreed to the establishment of the
League of Nations
The League of Nations (LN or LoN; , SdN) was the first worldwide intergovernmental organisation whose principal mission was to maintain world peace. It was founded on 10 January 1920 by the Paris Peace Conference (1919–1920), Paris Peace ...
on 25 January 1919. This came into being on 16 January 1920 with Britain, France, Italy and Japan as permanent members of the Executive Council; the
US Senate
The United States Senate is a chamber of the bicameral United States Congress; it is the upper house, with the U.S. House of Representatives being the lower house. Together, the Senate and House have the authority under Article One of the ...
voted against ratification of the treaty on 19 March, thus preventing the United States from joining the League.
Statistics
For similar statistics of the Central Powers, see
Central Powers#Statistics.
Principal powers
Britain

For much of the 19th century, Britain sought to maintain the European balance of power without formal alliances, a policy known as
splendid isolation. This left it dangerously exposed as Europe divided into opposing power blocs. In response, the
1895–1905 Conservative government negotiated first the 1902
Anglo-Japanese Alliance, then the 1904
Entente Cordiale with France. The first tangible result of this shift was British support for France against Germany in the
1905 Moroccan Crisis.
The
1905–1915 Liberal government continued this re-alignment with the 1907
Anglo-Russian Convention. Like the Anglo-Japanese and Entente agreements, it focused on settling colonial disputes but by doing so paved the way for wider co-operation and allowed Britain to refocus resources in response to
German naval expansion.

Since control of Belgium allowed an opponent to threaten invasion or blockade British trade, preventing it was a long-standing British strategic interest. Under Article VII of the 1839
Treaty of London, Britain guaranteed Belgian neutrality against aggression by any other state, by force if required. Chancellor
Theobald von Bethmann Hollweg
Theobald Theodor Friedrich Alfred von Bethmann Hollweg (29 November 1856 – 1 January 1921) was a German politician who was chancellor of the German Empire, imperial chancellor of the German Empire from 1909 to 1917. He oversaw the German entry ...
later dismissed this as a 'scrap of paper,' but British law officers routinely confirmed it as a binding legal obligation and its importance was well understood by Germany.
The 1911
Agadir Crisis
The Agadir Crisis, Agadir Incident, or Second Moroccan Crisis, was a brief crisis sparked by the deployment of a substantial force of French troops in the interior of Morocco in July 1911 and the deployment of the German gunboat to Agadir, ...
led to secret discussions between France and Britain in case of war with Germany. These agreed that within two weeks of its outbreak, a
British Expeditionary Force of 100,000 men would be landed in France; in addition, the
Royal Navy
The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
would be responsible for the
North Sea
The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...
, the
Channel and protecting Northern France, with the French navy concentrated in the
Mediterranean
The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...
. Britain was committed to support France in a war against Germany but this was not widely understood outside government or the upper ranks of the military.
As late as 1 August, a clear majority of the Liberal government and its supporters wanted to stay out of the war. While Liberal leaders
H. H. Asquith and
Edward Grey considered Britain legally and morally committed to support France regardless, waiting until Germany triggered the 1839 Treaty provided the best chance of preserving Liberal party unity.

The German high command was aware entering Belgium would lead to British intervention but decided the risk was acceptable; they expected a short war while their ambassador in London claimed troubles in Ireland would prevent Britain from assisting France.
On 3 August, Germany demanded unimpeded progress through any part of Belgium and when this was refused, invaded early on the morning of 4 August.
This changed the situation; the invasion of Belgium consolidated political and public support for the war by presenting what appeared to be a simple moral and strategic choice. The Belgians asked for assistance under the 1839 Treaty and in response, Britain declared war on Germany on 4 August 1914. Although Germany's violation of Belgium neutrality was not the only cause of British entry into the war, it was used extensively in government propaganda at home and abroad to make the case for British intervention. This confusion arguably persists today.
The declaration of war automatically involved all dominions and colonies and protectorates of the
British Empire
The British Empire comprised the dominions, Crown colony, colonies, protectorates, League of Nations mandate, mandates, and other Dependent territory, territories ruled or administered by the United Kingdom and its predecessor states. It bega ...
, many of whom made significant contributions to the Allied war effort, both in the provision of troops and civilian labourers. It was split into
Crown Colonies administered by the
Colonial Office in London, such as
Nigeria
Nigeria, officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf of Guinea in the Atlantic Ocean to the south. It covers an area of . With Demographics of Nigeria, ...
, and the self-governing
Dominion
A dominion was any of several largely self-governance, self-governing countries of the British Empire, once known collectively as the ''British Commonwealth of Nations''. Progressing from colonies, their degrees of self-governing colony, colon ...
s of
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
,
Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
,
New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
,
Newfoundland
Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the population ...
, and
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
. These controlled their own domestic policies and military expenditure but not foreign policy.
In terms of population, the largest component (after Britain herself) was the
British Raj
The British Raj ( ; from Hindustani language, Hindustani , 'reign', 'rule' or 'government') was the colonial rule of the British The Crown, Crown on the Indian subcontinent,
*
* lasting from 1858 to 1947.
*
* It is also called Crown rule ...
or British India, which included modern
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
,
Pakistan
Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...
,
Myanmar
Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and has ...
and
Bangladesh
Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...
. Unlike other colonies which came under the
Colonial Office, it was governed directly by the
India Office
The India Office was a British government department in London established in 1858 to oversee the administration of the Provinces of India, through the British viceroy and other officials. The administered territories comprised most of the mo ...
or by
princes loyal to the British; it also controlled British interests in the
Persian Gulf
The Persian Gulf, sometimes called the Arabian Gulf, is a Mediterranean seas, mediterranean sea in West Asia. The body of water is an extension of the Arabian Sea and the larger Indian Ocean located between Iran and the Arabian Peninsula.Un ...
, such as the
Trucial States
The Trucial States, also known as the Trucial Coast, the Trucial Sheikhdoms, or Trucial Oman, was a group of tribal confederations to the south of the Persian Gulf (southeastern Arabia) whose leaders had signed protective treaties, or truce ...
and
Oman
Oman, officially the Sultanate of Oman, is a country located on the southeastern coast of the Arabian Peninsula in West Asia and the Middle East. It shares land borders with Saudi Arabia, the United Arab Emirates, and Yemen. Oman’s coastline ...
. Over one million soldiers of the
British Indian Army served in different theatres of the war, primarily France and the
Middle East
The Middle East (term originally coined in English language) is a geopolitical region encompassing the Arabian Peninsula, the Levant, Turkey, Egypt, Iran, and Iraq.
The term came into widespread usage by the United Kingdom and western Eur ...
.
From 1914 to 1916, overall Imperial diplomatic, political and military strategy was controlled by the
British War Cabinet in London; in 1917 it was superseded by the
Imperial War Cabinet, which included representatives from the Dominions. Under the War Cabinet were the
Chief of the Imperial General Staff or CIGS, responsible for all Imperial ground forces, and the
Admiralty that did the same for the
Royal Navy
The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
. Theatre commanders like
Douglas Haig
Field marshal (United Kingdom), Field Marshal Douglas Haig, 1st Earl Haig (; 19 June 1861 – 29 January 1928) was a senior Officer (armed forces), officer of the British Army. During the First World War he commanded the British Expeditionary F ...
on the
Western Front or
Edmund Allenby in
Palestine
Palestine, officially the State of Palestine, is a country in West Asia. Recognized by International recognition of Palestine, 147 of the UN's 193 member states, it encompasses the Israeli-occupied West Bank, including East Jerusalem, and th ...
then reported to the CIGS.
After the Indian Army, the largest individual units were the
Australian Corps and
Canadian Corps
The Canadian Corps was a World War I corps formed from the Canadian Expeditionary Force in September 1915 after the arrival of the 2nd Canadian Division in France. The corps was expanded by the addition of the 3rd Canadian Division in December 19 ...
in France, which by 1918 were commanded by their own generals,
John Monash
General (Australia), General Sir John Monash (; 27 June 1865 – 8 October 1931) was an Australian civil engineer and military commander of the World War I, First World War. He commanded the 13th Brigade (Australia), 13th Infantry Brigade befor ...
and
Arthur Currie. Contingents from South Africa, New Zealand and Newfoundland served in theatres including France,
Gallipoli
The Gallipoli Peninsula (; ; ) is located in the southern part of East Thrace, the European part of Turkey, with the Aegean Sea to the west and the Dardanelles strait to the east.
Gallipoli is the Italian form of the Greek name (), meaning ' ...
,
German East Africa and the Middle East. Australian troops separately occupied
German New Guinea
German New Guinea () consisted of the northeastern part of the island of New Guinea and several nearby island groups, and was part of the German colonial empire. The mainland part of the territory, called , became a German protectorate in 188 ...
, with the South Africans doing the same in
German South West Africa; this resulted in the
Maritz rebellion by former Boers, which was quickly suppressed. After the war, New Guinea and South-West Africa became
Protectorate
A protectorate, in the context of international relations, is a State (polity), state that is under protection by another state for defence against aggression and other violations of law. It is a dependent territory that enjoys autonomy over ...
s, held until 1975 and 1990 respectively.
Russia

Between 1873 and 1887, Russia was allied with Germany and Austria-Hungary in the
League of the Three Emperors, then with Germany in the 1887–1890
Reinsurance Treaty; both collapsed due to the competing interests of Austria and Russia in the
Balkans
The Balkans ( , ), corresponding partially with the Balkan Peninsula, is a geographical area in southeastern Europe with various geographical and historical definitions. The region takes its name from the Balkan Mountains that stretch throug ...
. While France took advantage of this to agree the 1894
Franco-Russian Alliance, Britain viewed Russia with deep suspicion; in 1800, over 3,000 kilometres separated the Russian Empire and British India, by 1902, it was 30 km in some areas. This threatened to bring the two into direct conflict, as did the long-held Russian objective of gaining control of the
Bosporus Straits and with it access to the British-dominated
Mediterranean Sea
The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...
.

Defeat in the 1905 Russo-Japanese War and Britain's isolation during the 1899–1902
Second Boer War
The Second Boer War (, , 11 October 189931 May 1902), also known as the Boer War, Transvaal War, Anglo–Boer War, or South African War, was a conflict fought between the British Empire and the two Boer republics (the South African Republic and ...
led both parties to seek allies. The
Anglo-Russian Convention of 1907 settled disputes in Asia and allowed the establishment of the Triple Entente with France, which at this stage was largely informal. In 1908, Austria annexed the former Ottoman province of
Bosnia and Herzegovina
Bosnia and Herzegovina, sometimes known as Bosnia-Herzegovina and informally as Bosnia, is a country in Southeast Europe. Situated on the Balkans, Balkan Peninsula, it borders Serbia to the east, Montenegro to the southeast, and Croatia to th ...
; Russia responded by creating the
Balkan League in order to prevent further Austrian expansion.
In the 1912–1913
First Balkan War
The First Balkan War lasted from October 1912 to May 1913 and involved actions of the Balkan League (the Kingdoms of Kingdom of Bulgaria, Bulgaria, Kingdom of Serbia, Serbia, Kingdom of Greece, Greece and Kingdom of Montenegro, Montenegro) agai ...
,
Serbia
, image_flag = Flag of Serbia.svg
, national_motto =
, image_coat = Coat of arms of Serbia.svg
, national_anthem = ()
, image_map =
, map_caption = Location of Serbia (gree ...
,
Bulgaria
Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. It is situated on the eastern portion of the Balkans directly south of the Danube river and west of the Black Sea. Bulgaria is bordered by Greece and Turkey t ...
and
Greece
Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...
captured most of the remaining Ottoman possessions in Europe; disputes over the division of these resulted in the
Second Balkan War, in which Bulgaria was comprehensively defeated by its former allies.
Russia's industrial base and railway network had significantly improved since 1905, although from a relatively low base; in 1913,
Tsar Nicholas approved an increase in the Russian Army of over 500,000 men. Although there was no formal alliance between Russia and Serbia, their close bilateral links provided Russia with a route into the crumbling Ottoman Empire, where Germany also had significant interests. Combined with the increase in Russian military strength, both Austria and Germany felt threatened by Serbian expansion; when Austria invaded Serbia on 28 July 1914, Russian Foreign Minister
Sergey Sazonov viewed it as an Austro-German conspiracy to end Russian influence in the Balkans.
In addition to its own territory, Russia viewed itself as the defender of its fellow
Slavs
The Slavs or Slavic people are groups of people who speak Slavic languages. Slavs are geographically distributed throughout the northern parts of Eurasia; they predominantly inhabit Central Europe, Eastern Europe, Southeastern Europe, and ...
and on 30 July, mobilized in support of Serbia. In response, Germany declared war on Russia on 1 August, followed by Austria-Hungary on 6th; after Ottoman warships bombarded
Odessa
ODESSA is an American codename (from the German language, German: ''Organisation der ehemaligen SS-Angehörigen'', meaning: Organization of Former SS Members) coined in 1946 to cover Ratlines (World War II aftermath), Nazi underground escape-pl ...
in late October, the Entente declared war on the Ottoman Empire in November 1914.
France
French defeat in the 1870–1871
Franco-Prussian War
The Franco-Prussian War or Franco-German War, often referred to in France as the War of 1870, was a conflict between the Second French Empire and the North German Confederation led by the Kingdom of Prussia. Lasting from 19 July 1870 to 28 Janua ...
led to the loss of the two provinces of
Alsace-Lorraine and the establishment of the
Third Republic. The suppression of the
Paris Commune
The Paris Commune (, ) was a French revolutionary government that seized power in Paris on 18 March 1871 and controlled parts of the city until 28 May 1871. During the Franco-Prussian War of 1870–71, the French National Guard (France), Nation ...
by the new regime caused deep political divisions and led to a series of bitter political struggles, such as the
Dreyfus affair. As a result, aggressive nationalism or
Revanchism
Revanchism (, from ''revanche'', "revenge") is the political manifestation of the will to reverse the territorial losses which are incurred by a country, frequently after a war or after a social movement. As a term, ''revanchism'' originated i ...
was one of the few areas to unite the French.
The loss of Alsace-Lorraine deprived France of its natural defence line on the
Rhine
The Rhine ( ) is one of the List of rivers of Europe, major rivers in Europe. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps. It forms part of the Swiss-Liechtenstein border, then part of the Austria–Swit ...
, while it was weaker demographically than Germany, whose 1911 population was 64.9 million to 39.6 in France, which had the lowest birthrate in Europe. This meant that despite their very different political systems, when Germany allowed the Reinsurance Treaty to lapse, France seized the opportunity to agree the 1894
Franco-Russian Alliance. It also replaced Germany as the primary source of financing for Russian industry and the expansion of its railway network, particularly in border areas with Germany and Austria-Hungary.

However, Russian defeat in the 1904–1905
Russo-Japanese War
The Russo-Japanese War (8 February 1904 – 5 September 1905) was fought between the Russian Empire and the Empire of Japan over rival imperial ambitions in Manchuria and the Korean Empire. The major land battles of the war were fought on the ...
damaged its credibility, while Britain's isolation during the
Second Boer War
The Second Boer War (, , 11 October 189931 May 1902), also known as the Boer War, Transvaal War, Anglo–Boer War, or South African War, was a conflict fought between the British Empire and the two Boer republics (the South African Republic and ...
meant both countries sought additional allies. This resulted in the 1904
Entente Cordiale with Britain; like the 1907
Anglo-Russian Convention, for domestic British consumption it focused on settling colonial disputes but led to informal co-operation in other areas. By 1914, both the British army and
Royal Navy
The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
were committed to support France in the event of war with Germany but even in the British government, very few were aware of the extent of these commitments.

In response to Germany's declaration of war on Russia, France issued a general mobilisation in expectation of war on 2 August and on 3 August, Germany also declared war on France. Germany's ultimatum to Belgium brought Britain into the war on 4 August, although France did not declare war on Austria-Hungary until 12 August.
As with Britain, France's
colonies
A colony is a territory subject to a form of foreign rule, which rules the territory and its indigenous peoples separated from the foreign rulers, the colonizer, and their '' metropole'' (or "mother country"). This separated rule was often or ...
also became part of the war; pre-1914, French soldiers and politicians advocated using French African recruits to help compensate for France's demographic weakness. But it eventually proved useless, the soldiers from
Metropolitan France
Metropolitan France ( or ), also known as European France (), is the area of France which is geographically in Europe and chiefly comprises #Hexagon, the mainland, popularly known as "the Hexagon" ( or ), and Corsica. This collective name for the ...
still undertook all the tasks. From August to December 1914, the French lost nearly 300,000 dead on the Western Front, more than Britain suffered in the whole of WWII and the gaps were partly filled by colonial troops, over 500,000 of whom served on the Western Front over the period 1914–1918. Colonial troops also fought at
Gallipoli
The Gallipoli Peninsula (; ; ) is located in the southern part of East Thrace, the European part of Turkey, with the Aegean Sea to the west and the Dardanelles strait to the east.
Gallipoli is the Italian form of the Greek name (), meaning ' ...
, occupied
Togo
Togo, officially the Togolese Republic, is a country in West Africa. It is bordered by Ghana to Ghana–Togo border, the west, Benin to Benin–Togo border, the east and Burkina Faso to Burkina Faso–Togo border, the north. It is one of the le ...
and
Kamerun in West Africa and had a minor role in the Middle East, where France was the traditional protector of Christians in the Ottoman provinces of
Syria
Syria, officially the Syrian Arab Republic, is a country in West Asia located in the Eastern Mediterranean and the Levant. It borders the Mediterranean Sea to the west, Turkey to Syria–Turkey border, the north, Iraq to Iraq–Syria border, t ...
,
Palestine
Palestine, officially the State of Palestine, is a country in West Asia. Recognized by International recognition of Palestine, 147 of the UN's 193 member states, it encompasses the Israeli-occupied West Bank, including East Jerusalem, and th ...
and
Lebanon
Lebanon, officially the Republic of Lebanon, is a country in the Levant region of West Asia. Situated at the crossroads of the Mediterranean Basin and the Arabian Peninsula, it is bordered by Syria to the north and east, Israel to the south ...
.
Japan
Prior to the
Meiji Restoration
The , referred to at the time as the , and also known as the Meiji Renovation, Revolution, Regeneration, Reform, or Renewal, was a political event that restored Imperial House of Japan, imperial rule to Japan in 1868 under Emperor Meiji. Althoug ...
in 1868, Japan was a semi-feudal, largely agrarian state with few natural resources and limited technology. By 1914, it had transformed itself into a modern industrial state, with a powerful military; by defeating China in the
First Sino-Japanese War
The First Sino-Japanese War (25 July 189417 April 1895), or the First China–Japan War, was a conflict between the Qing dynasty of China and the Empire of Japan primarily over influence in Joseon, Korea. In Chinese it is commonly known as th ...
during 1894–1895, it established itself as the primary power in East Asia and colonised the then-unified Korea and
Formosa, now modern Taiwan.
Concerned by Russian expansion in Korea and
Manchuria
Manchuria is a historical region in northeast Asia encompassing the entirety of present-day northeast China and parts of the modern-day Russian Far East south of the Uda (Khabarovsk Krai), Uda River and the Tukuringra-Dzhagdy Ranges. The exact ...
, Britain and Japan signed the
Anglo-Japanese Alliance on 30 January 1902, agreeing if either were attacked by a third party, the other would remain neutral and if attacked by two or more opponents, the other would come to its aid. This meant Japan could rely on British support in a war with Russia, if either France or Germany, which also had interests in China, decided to join them. This gave Japan the reassurance needed to take on Russia in the 1905
Russo-Japanese War
The Russo-Japanese War (8 February 1904 – 5 September 1905) was fought between the Russian Empire and the Empire of Japan over rival imperial ambitions in Manchuria and the Korean Empire. The major land battles of the war were fought on the ...
; victory established Japan in the Chinese province of
Manchuria
Manchuria is a historical region in northeast Asia encompassing the entirety of present-day northeast China and parts of the modern-day Russian Far East south of the Uda (Khabarovsk Krai), Uda River and the Tukuringra-Dzhagdy Ranges. The exact ...
.

With Japan as an ally in the Far East,
John Fisher,
First Sea Lord
First Sea Lord, officially known as First Sea Lord and Chief of the Naval Staff (1SL/CNS), is the title of a statutory position in the British Armed Forces, held by an Admiral (Royal Navy), admiral or a General (United Kingdom), general of the ...
from 1904 to 1910, was able to refocus British naval resources in the
North Sea
The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...
to counter the threat from the
Imperial German Navy. The Alliance was renewed in 1911; in 1914, Japan joined the Entente in return for German territories in the Pacific, greatly annoying the Australian government which also wanted them.
On 7 August 1914, Britain officially asked for assistance in destroying German naval units in China and Japan formally declared war on Germany on 23 August 1914, followed by Austria-Hungary on 25 August 1914. On 2 September 1914, Japanese forces surrounded the German
Treaty Port of
Qingdao
Qingdao, Mandarin: , (Qingdao Mandarin: t͡ɕʰiŋ˧˩ tɒ˥) is a prefecture-level city in the eastern Shandong Province of China. Located on China's Yellow Sea coast, Qingdao was long an important fortress. In 1897, the city was ceded to G ...
, then known as Tsingtao, which surrendered on 7 November. The
Imperial Japanese Navy
The Imperial Japanese Navy (IJN; Kyūjitai: Shinjitai: ' 'Navy of the Greater Japanese Empire', or ''Nippon Kaigun'', 'Japanese Navy') was the navy of the Empire of Japan from 1868 to 1945, Potsdam Declaration, when it was dissolved followin ...
simultaneously occupied German colonies in the
Mariana,
Caroline, and
Marshall Islands
The Marshall Islands, officially the Republic of the Marshall Islands, is an island country west of the International Date Line and north of the equator in the Micronesia region of the Northwestern Pacific Ocean.
The territory consists of 29 c ...
, while in 1917, a Japanese naval squadron was sent to support the Allies in the
Mediterranean Sea
The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...
.
Japan's primary interest was in China and in January 1915, the Chinese government was presented with a secret ultimatum of
Twenty-One Demands
The Twenty-One Demands (; ) was a set of demands made during the World War I, First World War by the Empire of Japan under Prime Minister of Japan, Prime Minister Ōkuma Shigenobu to the Government of the Chinese Republic, government of the Re ...
, demanding extensive economic and political concessions. While these were eventually modified, the result was a surge of anti-Japanese
nationalism
Nationalism is an idea or movement that holds that the nation should be congruent with the state. As a movement, it presupposes the existence and tends to promote the interests of a particular nation, Smith, Anthony. ''Nationalism: Theory, I ...
in China and an economic boycott of Japanese goods. In addition, the other Allies now saw Japan as a threat, rather than a partner, lead to tensions first with Russia, then the US after it entered the war in April 1917. Despite protests from the other Allies, after the war Japan refused to return Qingdao and the province of
Shandong
Shandong is a coastal Provinces of China, province in East China. Shandong has played a major role in Chinese history since the beginning of Chinese civilization along the lower reaches of the Yellow River. It has served as a pivotal cultural ...
to China.
Italy

The 1882
Triple Alliance between Germany, Austria-Hungary and Italy was renewed at regular intervals, but was compromised by conflicting objectives between Italy and Austria in the
Adriatic and
Aegean seas. Italian nationalists referred to Austrian-held
Istria
Istria ( ; Croatian language, Croatian and Slovene language, Slovene: ; Italian language, Italian and Venetian language, Venetian: ; ; Istro-Romanian language, Istro-Romanian: ; ; ) is the largest peninsula within the Adriatic Sea. Located at th ...
(including
Trieste
Trieste ( , ; ) is a city and seaport in northeastern Italy. It is the capital and largest city of the Regions of Italy#Autonomous regions with special statute, autonomous region of Friuli-Venezia Giulia, as well as of the Province of Trieste, ...
and
Fiume
Rijeka (;
Fiume ( �fjuːme in Italian and in Fiuman Venetian) is the principal seaport and the third-largest city in Croatia. It is located in Primorje-Gorski Kotar County on Kvarner Bay, an inlet of the Adriatic Sea and in 2021 had a po ...
) and
Trento
Trento ( or ; Ladin language, Ladin and ; ; ; ; ; ), also known in English as Trent, is a city on the Adige, Adige River in Trentino-Alto Adige/Südtirol in Italy. It is the capital of the Trentino, autonomous province of Trento. In the 16th ...
as
'the lost territories', making the Alliance so controversial that the terms were kept secret until it expired in 1915.
Alberto Pollio, the pro-Austrian
Chief of Staff of the Italian Army, died on 1 July 1914, taking many of the prospects for Italian support with him. The Italian Prime Minister
Antonio Salandra argued that as the Alliance was defensive in nature, Austria's aggression against Serbia and Italy's exclusion from the decision-making process meant it was not obliged to join them.
[Hamilton, Richard F; Herwig, Holger H. ''Decisions for War, 1914–1917''. p. 194.]
His caution was understandable because France and Britain either supplied or controlled the import of most of Italy's raw materials, including 90% of its coal.
Salandra described the process of choosing a side as 'sacred egoism,' but as the war was expected to end before mid-1915 at the latest, making this decision became increasingly urgent. In line with Italy's obligations under the Triple Alliance, the bulk of the army was concentrated on Italy's border with France; in October, Pollio's replacement,
General Luigi Cadorna, was ordered to begin moving these troops to the North-Eastern one with Austria.
Under the April 1915
Treaty of London, Italy agreed to join the Entente in return for Italian-populated territories of Austria-Hungary and other concessions; in return, it declared war on Austria-Hungary in May 1915 as required, although not on Germany until 1916.
[Hamilton, Richard F; Herwig, Holger H. ''Decisions for War, 1914–1917''. pp. 194–198.] Italian resentment at the difference between the promises of 1915 and the actual results of the 1919
Treaty of Versailles
The Treaty of Versailles was a peace treaty signed on 28 June 1919. As the most important treaty of World War I, it ended the state of war between Germany and most of the Allies of World War I, Allied Powers. It was signed in the Palace ...
would be powerful factors in the rise of
Benito Mussolini
Benito Amilcare Andrea Mussolini (29 July 188328 April 1945) was an Italian politician and journalist who, upon assuming office as Prime Minister of Italy, Prime Minister, became the dictator of Fascist Italy from the March on Rome in 1922 un ...
.
Affiliated state combatants
Serbia
In 1817, the
Principality of Serbia
The Principality of Serbia () was an autonomous, later sovereign state in the Balkans that came into existence as a result of the Serbian Revolution, which lasted between 1804 and 1817. Its creation was negotiated first through an unwritten agre ...
became an autonomous province within the
Ottoman Empire
The Ottoman Empire (), also called the Turkish Empire, was an empire, imperial realm that controlled much of Southeast Europe, West Asia, and North Africa from the 14th to early 20th centuries; it also controlled parts of southeastern Centr ...
; with Russian support, it gained full independence after the 1877–1878
Russo-Turkish War. Many Serbs viewed Russia as protector of the
South Slavs
South Slavs are Slavic people who speak South Slavic languages and inhabit a contiguous region of Southeast Europe comprising the eastern Alps and the Balkan Peninsula. Geographically separated from the West Slavs and East Slavs by Austria, ...
in general but also specifically against Bulgaria, where Russian objectives increasingly collided with
Bulgarian nationalism.
When Austria annexed Bosnia and Herzegovina in 1908, Russia responded by creating the
Balkan League to prevent further Austrian expansion.
Austria viewed Serbia with hostility partly due to its links with Russia, whose claim to be the protector of South Slavs extended to those within the Austro-Hungarian Empire, such as the
Czechs
The Czechs (, ; singular Czech, masculine: ''Čech'' , singular feminine: ''Češka'' ), or the Czech people (), are a West Slavs, West Slavic ethnic group and a nation native to the Czech Republic in Central Europe, who share a common Bohemia ...
and
Slovaks
The Slovaks ( (historical Sloveni ), singular: ''Slovák'' (historical: ''Sloven'' ), feminine: ''Slovenka'' , plural: ''Slovenky'') are a West Slavic ethnic group and nation native to Slovakia who share a common ancestry, culture, history ...
. Serbia also potentially gave Russia the ability to achieve their long-held objective of capturing
Constantinople
Constantinople (#Names of Constantinople, see other names) was a historical city located on the Bosporus that served as the capital of the Roman Empire, Roman, Byzantine Empire, Byzantine, Latin Empire, Latin, and Ottoman Empire, Ottoman empire ...
and the
Dardanelles
The Dardanelles ( ; ; ), also known as the Strait of Gallipoli (after the Gallipoli peninsula) and in classical antiquity as the Hellespont ( ; ), is a narrow, natural strait and internationally significant waterway in northwestern Turkey th ...
.

Austria-Hungary supported the idea of an
independent Albania, since this would prevent Serbian access to the Austrian-controlled
Adriatic Sea
The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkans, Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Se ...
. The success of the
Albanian revolt in 1912 threatened Serbian ambitions for the incorporation of "
Old Serbia" into its domain and exposed the weakness of the Ottoman Empire. This led to the outbreak of the
First Balkan War
The First Balkan War lasted from October 1912 to May 1913 and involved actions of the Balkan League (the Kingdoms of Kingdom of Bulgaria, Bulgaria, Kingdom of Serbia, Serbia, Kingdom of Greece, Greece and Kingdom of Montenegro, Montenegro) agai ...
, with
Serbia
, image_flag = Flag of Serbia.svg
, national_motto =
, image_coat = Coat of arms of Serbia.svg
, national_anthem = ()
, image_map =
, map_caption = Location of Serbia (gree ...
,
Montenegro
, image_flag = Flag of Montenegro.svg
, image_coat = Coat of arms of Montenegro.svg
, coa_size = 80
, national_motto =
, national_anthem = ()
, image_map = Europe-Mont ...
,
Bulgaria
Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. It is situated on the eastern portion of the Balkans directly south of the Danube river and west of the Black Sea. Bulgaria is bordered by Greece and Turkey t ...
and
Greece
Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...
capturing most of the remaining Ottoman possessions in Europe. Disputes over the division of these resulted in the
Second Balkan War, in which Bulgaria was comprehensively defeated by its former allies.
As a result of the 1913
Treaty of Bucharest, Serbia increased its territory by 100% and its population by 64%. However, it now faced a hostile Austria-Hungary, a resentful Bulgaria and
resistance in its conquered territories. Germany too had ambitions in the Ottoman Empire, the centrepiece being the planned
Berlin–Baghdad railway, with Serbia the only section not controlled by a pro-German state.
The exact role played by Serbian officials in the
assassination of Archduke Franz Ferdinand
The assassination of Archduke Franz Ferdinand was one of the key events that led to World War I. Archduke Franz Ferdinand of Austria, heir presumptive to the Austria-Hungary, Austro-Hungarian throne, and his wife, Sophie, Duchess of Hohenberg ...
is still debated but despite complying with most of their demands, Austria-Hungary invaded on 28 July 1914. While Serbia successfully repulsed the Austro-Hungarian army in 1914, it was exhausted by the two Balkan Wars and unable to replace its losses of men and equipment. In 1915, Bulgaria joined the Central Powers and by the end of the year, a combined Bulgar-Austrian-German army occupied most of Serbia. Between 1914 and 1918, Serbia suffered the greatest proportional losses of any combatant, with over 25% of all those mobilised becoming casualties; including civilians and deaths from disease, over 1.2 million died, nearly 30% of the entire population.
Belgium
In 1830, the southern provinces of the Netherlands broke away to form the
Kingdom of Belgium
Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southe ...
and their independence was confirmed by the 1839
Treaty of London. Article VII of the Treaty required Belgium to remain perpetually neutral and committed Austria, France, Germany and Russia to guarantee that against aggression by any other state, including the signatories.
While the French and German militaries accepted Germany would almost certainly violate Belgian neutrality in the event of war, the extent of that was unclear. The original
Schlieffen Plan only required a limited incursion into the Belgian
Ardennes, rather than a full-scale invasion; in September 1911, the Belgian Foreign Minister told a British Embassy official they would not call for assistance if the Germans limited themselves to that.
While neither Britain or France could allow Germany to occupy Belgium unopposed, a Belgian refusal to ask for help would complicate matters for the
British Liberal government, which contained a significant isolationist element.
However, the key German objective was to avoid war on two fronts; France had to be defeated before Russia could fully mobilise and give time for German forces to be transferred to the East. The growth of the Russian railway network and increase in speed of mobilisation made rapid victory over France even more important; to accommodate the additional 170,000 troops approved by the 1913 Army Bill, the 'incursion' now became a full-scale invasion. The Germans accepted the risk of British intervention; in common with most of Europe, they expected it to be a short war while their London Ambassador claimed civil war in Ireland would prevent Britain from assisting its Entente partners.
On 3 August, a German ultimatum demanded unimpeded progress through any part of Belgium, which was refused. Early on the morning of 4 August, the Germans invaded and the Belgian government called for British assistance under the 1839 Treaty; by the end of 1914, over 95% of the country was occupied but the Belgian Army held their lines on the
Yser Front throughout the war.
In the
Belgian Congo
The Belgian Congo (, ; ) was a Belgian colonial empire, Belgian colony in Central Africa from 1908 until independence in 1960 and became the Republic of the Congo (Léopoldville). The former colony adopted its present name, the Democratic Repu ...
, 25,000 Congolese troops plus an estimated 260,000 porters joined British forces in the 1916
East African Campaign. By 1917, they controlled the western part of
German East Africa which would become the Belgian
League of Nations Mandate of
Ruanda-Urundi or modern-day
Rwanda
Rwanda, officially the Republic of Rwanda, is a landlocked country in the Great Rift Valley of East Africa, where the African Great Lakes region and Southeast Africa converge. Located a few degrees south of the Equator, Rwanda is bordered by ...
and
Burundi
Burundi, officially the Republic of Burundi, is a landlocked country in East Africa. It is located in the Great Rift Valley at the junction between the African Great Lakes region and Southeast Africa, with a population of over 14 million peop ...
.
Greece

Greece almost doubled in size as a result of the
Balkan Wars
The Balkan Wars were two conflicts that took place in the Balkans, Balkan states in 1912 and 1913. In the First Balkan War, the four Balkan states of Kingdom of Greece (Glücksburg), Greece, Kingdom of Serbia, Serbia, Kingdom of Montenegro, M ...
of 1912 and 1913, but the success masked deep divisions within the political elite. In 1908, the island of
Crete
Crete ( ; , Modern Greek, Modern: , Ancient Greek, Ancient: ) is the largest and most populous of the Greek islands, the List of islands by area, 88th largest island in the world and the List of islands in the Mediterranean#By area, fifth la ...
, formally part of the
Ottoman Empire
The Ottoman Empire (), also called the Turkish Empire, was an empire, imperial realm that controlled much of Southeast Europe, West Asia, and North Africa from the 14th to early 20th centuries; it also controlled parts of southeastern Centr ...
but administered by Greek officials, declared union with Greece, led by the charismatic nationalist
Eleftherios Venizelos. A year later, young army officers formed the Military League to advocate for an aggressive and expansionist foreign policy; with their backing, Venizelos won a majority in the 1910 Parliamentary elections, followed by another in 1912. He had effectively broken the power of the pre-1910 political class and his position was then further strengthened by success in the Balkan Wars.
In 1913, the Greek monarch
George I was assassinated; he was succeeded by his son
Constantine who had attended
Heidelberg University, served in a Prussian regiment and married
Sophia of Prussia, sister of Emperor
William II. These links and a belief the Central Powers would win the war combined to make Constantine pro-German.
Venizelos himself favoured the Entente, partly due to their ability to block the maritime trade routes required for Greek imports.

Other issues adding complexity to this decision included disputes with Bulgaria and Serbia over the regions of
Thrace
Thrace (, ; ; ; ) is a geographical and historical region in Southeast Europe roughly corresponding to the province of Thrace in the Roman Empire. Bounded by the Balkan Mountains to the north, the Aegean Sea to the south, and the Black Se ...
and
Macedonia as well as control of the
Aegean Islands. Greece captured most of the islands during the Balkan Wars but Italy occupied the
Dodecanese
The Dodecanese (, ; , ''Dodekánisa'' , ) are a group of 15 larger and 150 smaller Greek islands in the southeastern Aegean Sea and Eastern Mediterranean, off the coast of Anatolia, of which 26 are inhabited. This island group generally define ...
in 1912 and was in no hurry to give them back, while the Ottomans demanded the return of many others. In general, the Triple Entente favoured Greece, the Triple Alliance backed the Ottomans; Greece ultimately gained the vast majority but Italy did not cede the Dodecanese until 1947, while others remain
disputed even today.
As a result, Greece initially remained neutral but in March 1915, the Entente offered concessions to join the
Dardanelles
The Dardanelles ( ; ; ), also known as the Strait of Gallipoli (after the Gallipoli peninsula) and in classical antiquity as the Hellespont ( ; ), is a narrow, natural strait and internationally significant waterway in northwestern Turkey th ...
campaign. Arguments over whether to accept led to the
National Schism, with an Entente-backed administration under Venizelos in Crete, and a Royalist one led by Constantine in
Athens
Athens ( ) is the Capital city, capital and List of cities and towns in Greece, largest city of Greece. A significant coastal urban area in the Mediterranean, Athens is also the capital of the Attica (region), Attica region and is the southe ...
that supported the Central Powers.
In September 1915, Bulgaria joined the Central Powers; in October, Venizelos allowed Entente forces to land at
Thessaloniki or Salonica to support the Serbs, although they were too late to prevent their defeat. In August 1916, Bulgarian troops advanced into Greek-held Macedonia and Constantine ordered the army not to resist; anger at this led to a coup and he was eventually forced into exile in June 1917. A new national government under Venizelos joined the Entente, while the Greek
National Defence Army Corps fought with the Allies on the
Macedonian front.
Montenegro

Unlike Serbia, with whom it shared close cultural and political connections, the
Kingdom of Montenegro gained little from its participation in the 1912–1913 Balkan Wars. The main Montenegrin offensive was in
Ottoman-controlled Albania, where it suffered heavy losses during the seven month
Siege of Scutari. Austria-Hungary opposed Serb or Montenegrin control of Albania, since it provided access to the
Adriatic Sea
The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkans, Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Se ...
; despite Scutari's surrender, Montenegro was forced to relinquish it by the
1913 Treaty of London and it became capital of the short-lived
Principality of Albania. This was largely an Austrian creation; the new ruler,
William, Prince of Albania, was a German who was forced into exile in September, only seven months after taking up his new position and later served with the
Imperial German Army
The Imperial German Army (1871–1919), officially referred to as the German Army (), was the unified ground and air force of the German Empire. It was established in 1871 with the political unification of Germany under the leadership of Kingdom o ...
.
In addition to the lack of substantive gains from the Balkan Wars, there were long-running internal divisions between those who like
Nicholas I preferred an independent Montenegro and those who advocated union with Serbia. In July 1914, Montenegro was not only militarily and economically exhausted, but also faced a multitude of political, economic and social issues.
At meetings held in March 1914, Austria-Hungary and Germany agreed union with Serbia must be prevented; Montenegro could either remain independent or be divided, its coastal areas becoming part of Albania, while the rest could join Serbia.
Nicholas seriously considered neutrality as a way to preserve his dynasty and on 31 July notified the Russian Ambassador Montenegro would only respond to an Austrian attack. He also held discussions with Austria, proposing neutrality or even active support in return for territorial concessions in Albania.
However, close links between the Serbian and Montenegrin militaries as well as popular sentiment meant there was little support for remaining neutral, especially after Russia joined the war; on 1 August, the National Assembly declared war on Austria-Hungary in fulfilment of its obligations to Serbia. After some initial success, in January 1916, the Montenegrin Army was forced to surrender to an Austro-Hungarian force.
Beda
The
Beda Sultanate was invaded by Ottoman forces in February 1915 and March 1916.
Britain assisted the Beda Sultanate in defeating the Ottoman invasions by sending arms and ammunition.
Asir
The
Idrisid Emirate of Asir participated in the
Arab Revolt. Its Emir,
Muhammad ibn Ali al-Idrisi, signed an agreement with the British and joined the Allies in May 1915.
Nejd and Hasa
The
Emirate of Nejd and Hasa launched a failed offensive against the Ottoman aligned Emirate of Jabal Shammar in January 1915. It then agreed to enter the war as an ally of Britain in the
Treaty of Darin on 26 December 1915.
Romania

Equal status with the main Entente Powers was one of the primary conditions for Romania's entry into the War. The Powers officially recognised this status through the
1916 Treaty of Bucharest. Romania fought on three of the four European Fronts:
Eastern,
Balkan and
Italian, fielding in total over 1,200,000 troops.
Romanian military industry was mainly focused on converting various fortification guns into field and anti-aircraft artillery. Up to 334 German 53 mm
Fahrpanzer guns, 93 French 57 mm Hotchkiss guns, 66 Krupp 150 mm guns, and dozens more 210 mm guns were mounted on Romanian-built
carriages and transformed into mobile field artillery, with 45 Krupp 75 mm guns and 132 Hotchkiss 57 mm guns being transformed into anti-aircraft artillery. The Romanians also
upgraded 120 German Krupp 105 mm howitzers, the result being the most effective field howitzer in Europe at that time. Romania even managed to design and build from scratch its own model of mortar, the 250 mm Negrei Model 1916.
Other Romanian technological assets include the building of
Vlaicu III, the world's first aircraft made of metal. The Romanian Navy possessed the largest warships on the Danube. They were a class of four river monitors, built locally at the
Galați shipyard using parts manufactured in Austria-Hungary. The first one launched was ''Lascăr Catargiu'', in 1907. The Romanian monitors displaced almost 700 tons, were armed with three 120 mm naval guns in three turrets, two 120 mm naval howitzers, four 47 mm anti-aircraft guns and two 6.5 machine guns. The monitors took part in the
Battle of Turtucaia and the
First Battle of Cobadin. The Romanian-designed Schneider 150 mm Model 1912 howitzer was considered one of the most modern field guns on the Western Front.
Romania's entry into the War in August 1916 provoked major changes for the Germans. General
Erich von Falkenhayn was dismissed and sent to command the Central Powers forces in Romania, which enabled
Hindenburg's subsequent ascension to power. Due to having to fight against all of the Central Powers on the longest front in Europe (1,600 km) and with little foreign help (only 50,000 Russians aided 650,000 Romanians in 1916),
the Romanian capital was conquered that December. Vlaicu III was also captured and shipped to Germany, being last seen in 1942. The Romanian administration established a new capital at
Iași
Iași ( , , ; also known by other #Etymology and names, alternative names), also referred to mostly historically as Jassy ( , ), is the Cities in Romania, third largest city in Romania and the seat of Iași County. Located in the historical ...
and continued to fight on the Allied side in 1917. Despite being relatively short, the Romanian campaign of 1916 provided considerable respite for the Western Allies, as the Germans ceased all their other offensive operations in order to deal with Romania. After suffering a tactical defeat against the Romanians (aided by Russians) in July 1917 at
Mărăști, the Central Powers launched two counterattacks, at
Mărășești and
Oituz. The German offensive at Mărășești was soundly defeated, with German prisoners later telling their Romanian captors that German casualties were extremely heavy, and that they "had not encountered such stiff resistance since the battles of Somme and Verdun". The Austro-Hungarian offensive at Oituz also failed. On 22 September, the Austro-Hungarian
''Enns''-class river monitor
SMS ''Inn'' was sunk by a Romanian mine near Brăila. After Russia signed the
Treaty of Brest-Litovsk and dropped out of the War, Romania was left surrounded by the Central Powers and eventually signed a
similar treaty on 7 May 1918. Despite being forced to cede land to Austria-Hungary and Bulgaria, Romania ended up with a net gain in territory due to the
Union with Bessarabia. On 10 November, Romania re-entered the War and fought a
war with Hungary that lasted until August 1919.
Republic of the United States of Brazil
Brazil entered the war in 1917 after the United States intervened on the basis of Germany's unrestricted submarine warfare sinking its merchant ships, which Brazil also cited as a reason to enter the war fighting against Germany and the Central Powers. The
First Brazilian Republic sent the Naval Division in War Operations that joined the British fleet in
Gibraltar
Gibraltar ( , ) is a British Overseas Territories, British Overseas Territory and British overseas cities, city located at the southern tip of the Iberian Peninsula, on the Bay of Gibraltar, near the exit of the Mediterranean Sea into the A ...
and made the first Brazilian naval effort in international waters. In compliance with the commitments made at the
Inter-American Conference, held in Paris from 20 November to 3 December 1917, the Brazilian Government sent a medical mission composed of civilian and military surgeons to work in field hospitals of the European theatre, a contingent of sergeants and officers to serve with the
French Army
The French Army, officially known as the Land Army (, , ), is the principal Army, land warfare force of France, and the largest component of the French Armed Forces; it is responsible to the Government of France, alongside the French Navy, Fren ...
; Airmen from the Army and Navy to join the
Royal Air Force
The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
, and the employment of part of the Fleet, primarily in the anti-submarine war.
Co-belligerents: the United States
The
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
declared war on Germany in April 1917 on the grounds that Germany violated US neutrality by attacking international shipping with its
unrestricted submarine warfare campaign.
The remotely connected
Zimmermann Telegram of the same period, within which the Germans promised to help Mexico regain some of its territory
lost to the US nearly seven decades before in the event of the United States entering the war, was
also a contributing factor.
The US entered the war as an "associated power", rather than a formal ally of
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
and the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
, in order to avoid "foreign entanglements".
[Tucker&Roberts pp. 1232, 1264, 1559] Although the
Ottoman Empire
The Ottoman Empire (), also called the Turkish Empire, was an empire, imperial realm that controlled much of Southeast Europe, West Asia, and North Africa from the 14th to early 20th centuries; it also controlled parts of southeastern Centr ...
and
Bulgaria
Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. It is situated on the eastern portion of the Balkans directly south of the Danube river and west of the Black Sea. Bulgaria is bordered by Greece and Turkey t ...
severed relations with the United States, neither declared war,
[Tucker&Roberts p. 1559] nor did
Austria-Hungary
Austria-Hungary, also referred to as the Austro-Hungarian Empire, the Dual Monarchy or the Habsburg Monarchy, was a multi-national constitutional monarchy in Central Europe#Before World War I, Central Europe between 1867 and 1918. A military ...
. Eventually, however, the United States also
declared war on Austria-Hungary in December 1917, predominantly to help hard-pressed Italy.
Non-state combatants
Three non-state combatants, which voluntarily fought with the Allies and seceded from the constituent states of the Central Powers at the end of the war, were allowed to participate as winning nations to the peace treaties:
*
Armenian
Armenian may refer to:
* Something of, from, or related to Armenia, a country in the South Caucasus region of Eurasia
* Armenians, the national people of Armenia, or people of Armenian descent
** Armenian diaspora, Armenian communities around the ...
irregulars
Irregular military is any military component distinct from a country's regular armed forces, representing non-standard militant elements outside of conventional governmental backing. Irregular elements can consist of militias, private army, pr ...
and
volunteers
Volunteering is an elective and freely chosen act of an individual or group giving their time and labor, often for community service. Many volunteers are specifically trained in the areas they work, such as medicine, education, or emergenc ...
: seceded from the Russian Empire in the aftermath of the Russian Revolution and fought against the Ottoman Empire
*
Assyrian volunteers under
Mar Shimun XIX Benyamin and the Assyrian tribal chiefs decided to side with the Allies, first with Russia, and next with the British, in the hope that they might secure after the victory, self-government for the Assyrians. The French also joined the alliance with the Assyrians, offering them 20,000 rifles, and the Assyrian army grew to 20,000 men co-led by
Agha Petros of the Bit-
Bazi tribe, and
Malik Khoshaba of the Bit-
Tiyari tribe.
[Paul Bartrop, Encountering Genocide: Personal Accounts from Victims, Perpetrators, and Witnesses, ABC-CLIO, 2014]
*
Polish Legions
*
Czechoslovak Legions: armed by
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
,
Italy
Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
, and Russia
Additionally, there were also several
Kurdish rebellions during World War I. Most of these, except for the uprisings of August 1917, were not supported by any of the Allied powers.
Leaders
Serbia
*
Peter I –
King of Serbia
*
Crown Prince Alexander – Regent, Commander-in-Chief
*
Nikola Pašić –
Prime Minister of Serbia
The prime minister of Serbia ( sr-Cyrl, премијер Србије, premijer Srbije; feminine gender, feminine: премијерка/premijerka), officially the president of the Government of the Republic of Serbia ( sr-Cyrl, председн ...
*
Field Marshal
Field marshal (or field-marshal, abbreviated as FM) is the most senior military rank, senior to the general officer ranks. Usually, it is the highest rank in an army (in countries without the rank of Generalissimo), and as such, few persons a ...
Radomir Putnik –
Chief of the General Staff of the
Serbian Army (1914–1915)
* General/Field Marshal
Živojin Mišić – Deputy Chief of the General Staff (1914), Commander of
First Army (1914–1915; 1917), later Chief of the General Staff (1918)
* General/
Field Marshal
Field marshal (or field-marshal, abbreviated as FM) is the most senior military rank, senior to the general officer ranks. Usually, it is the highest rank in an army (in countries without the rank of Generalissimo), and as such, few persons a ...
Petar Bojović – Commander of the
First Army (1914), Deputy Chief of General Staff (1915–1916), Chief of the General Staff (1916–1917) later Commander of the First Army (1918)
* General/
Field Marshal
Field marshal (or field-marshal, abbreviated as FM) is the most senior military rank, senior to the general officer ranks. Usually, it is the highest rank in an army (in countries without the rank of Generalissimo), and as such, few persons a ...
Stepa Stepanović – Commander of the
Second Army (1914–1918)
* General
Pavle Jurišić Šturm – Commander of the
Third Army (1914–1916)
* Colonel –
Minister of War
A ministry of defence or defense (see American and British English spelling differences#-ce.2C -se, spelling differences), also known as a department of defence or defense, is the part of a government responsible for matters of defence and Mi ...
(1914)
* Colonel – Minister of War (1914–1915)
* Colonel/General – Minister of War (1915–1918)
* General
Mihailo Rašić – Minister of War (1918)
* Colonel/General
Miloš Vasić – Commander of the First Army (1916; 1917), Commander of the Third Army (1916)
Montenegro
*
Nicholas I –
King of Montenegro, Commander-in-Chief
* General
Serdar
Serdar may refer to
* Serdar (given name)
* Serdar (surname) Serdar is a surname of the following notable people:
* Can Serdar (born 1996), German-Turkish football midfielder
* Emerîkê Serdar (1935–2018), Kurdish-Yezidi writer from Armenia
* I ...
Janko Vukotić –
Prime Minister
A prime minister or chief of cabinet is the head of the cabinet and the leader of the ministers in the executive branch of government, often in a parliamentary or semi-presidential system. A prime minister is not the head of state, but r ...
, Commander of the 1st Montenegrin Army
* General
Božidar Janković – Chief of the General Staff of the Montenegrin Army (1914–1915)
* Colonel
Petar Pešić – Deputy Chief of the General Staff of the Montenegrin Army (1914–1915), later Chief of the General Staff of the Montenegrin Army (1915–1916)
*
Crown Prince Danilo II Petrović-Njegoš – in the staff of the 1st Montenegrin Army
* Brigadier
Krsto Popović – in the staff of the 1st Montenegrin Army,
Aide-de-camp to Serdar Janko Vukotić
* General
Anto Gvozdenović – King's Aide-de-camp
* General
Mitar Martinović – commander of several detachments in the Montenegrin Army (Drina and Herzegovina detachments together in 1914–1915, Kotor detachment in 1916)
Russia (1914–1917)

*
Nicholas II –
Russian Emperor,
King of Poland
Poland was ruled at various times either by dukes and princes (10th to 14th centuries) or by kings (11th to 18th centuries). During the latter period, a tradition of Royal elections in Poland, free election of monarchs made it a uniquely electab ...
, and
Grand Duke of Finland (until 15 March 1917)
* Grand Duke Nicholas Nikolaevich of Russia (1856–1929), Grand Duke Nicholas Nikolaevich – Commander-in-Chief (1 August 1914 – 5 September 1916) and viceroy in the Caucasus
* Ivan Goremykin – List of heads of government of Russia, Chairmen of Council of Ministers of the Russian Empire (1 August 1914 – 2 February 1916)
* Boris Shturmer, Boris Stürmer – Chairmen of Council of Ministers of the Russian Empire (2 February 1916 – 23 November 1916)
* Alexander Trepov – Chairmen of Council of Ministers of the Russian Empire (23 November 1916 – 27 December 1916)
* Nikolai Golitsyn – Chairmen of Council of Ministers of the Russian Empire (27 December 1916 – 9 January 1917)
* General of the Cavalry Alexander Samsonov – Commander of the 2nd Army (Russian Empire), Russian Second Army for the invasion of East Prussia (1 August 1914 – 29 August 1914)
* General of the Cavalry Paul von Rennenkampf – Commander of the 1st Army (Russian Empire), Russian First Army for the invasion of East Prussia (1 August 1914 – November 1914)
* General of the Artillery (Imperial Russia), General of the Artillery Nikolai Ivanov (general), Nikolay Ivanov – Commander of the Russian Army on the Southwestern Front (Russian Empire), Southwestern Front, (1 August 1914 – March 1916) responsible for much of the action in Galicia (Eastern Europe), Galicia
* Adjutant general, General Adjutant Aleksei Brusilov – Commander of the Southwestenr Front, then provisional Commander-in-Chief after the Tsar's abdication (February 1917 – August 1917)
* General of the Infantry (Imperial Russia), General of the Infantry Lavr Kornilov, Lavr Georgievich Kornilov – Commander of the Southwestern Front, then Commander-in-Chief (August 1917)
* General of the Infantry Aleksey Kuropatkin – Commander of the Northern Front (Russian Empire), Northern Front (October 1915 – 1917)
* General of the Infantry Nikolai Yudenich – Commander of the Caucasus (January 1915 – May 1917)
* List of Russian admirals, Admiral Andrei Eberhardt – Commander of the Black Sea Fleet (1914–16)
* Admiral Alexander Kolchak – Commander of the Black Sea Fleet (1916–17)
* Admiral Nikolai Ottovich von Essen, Nikolai Essen – Commander of the Baltic Fleet (1913 – May 1915)
Belgium
* Albert I of Belgium – Monarchy of Belgium, King of the Belgians (23 December 1909 – 17 February 1934) and Commander-in-Chief of the Belgian Army
* Charles de Broqueville – Prime Minister of Belgium, Prime Minister (1912–1918); replaced by Gérard Cooreman in June 1918 shortly before the end of the war.
* Félix Wielemans – Chief of Staff of the Belgian Army
* Gérard Leman – general commanding the Battle of Liège, defense of Liège
* Charles Tombeur – commander of the colonial ''Force Publique'' in the East African campaign (World War I), East African theatre
France
* Raymond Poincaré – President of France
* René Viviani – Prime Minister of France (13 June 1914 – 29 October 1915)
* Aristide Briand – Prime Minister of France (29 October 1915 – 20 March 1917)
* Alexandre Ribot – Prime Minister of France (20 March 1917 – 12 September 1917)
* Paul Painlevé – Prime Minister of France (12 September 1917 – 16 November 1917)
* Georges Clemenceau – Prime Minister of France (from 16 November 1917)
* Divisional general, Divisional General/Marshal of France, Marshal Joseph Joffre – Commander-in-Chief of the
French Army
The French Army, officially known as the Land Army (, , ), is the principal Army, land warfare force of France, and the largest component of the French Armed Forces; it is responsible to the Government of France, alongside the French Navy, Fren ...
(3 August 1914 – 13 December 1916)
* Divisional General Robert Nivelle – Commander-in-Chief of the French Army (13 December 1916 – April 1917)
* Divisional General/Marshal Philippe Pétain – Commander-in-Chief of the French Army (April 1917 – 11 November 1918)
* Divisional General/Marshal Ferdinand Foch – Supreme Allied Commander (26 March 1918 – 11 November 1918)
* Divisional General Maurice Sarrail – Commander of the Allied armies at the Macedonian front, Salonika front (1915–1917)
* Army general (France), Army General Adolphe Guillaumat – Commander of the Allied armies at the Salonika front (1917–1918)
* Divisional General/Marshal Louis Franchet d'Espèrey – Commander of the Allied armies at the Salonika front (1918)
* Brigadier General Milan Rastislav Štefánik – general of the French Army, Commander of the Czechoslovak Legions
Britain and the British Empire
United Kingdom
* George V – Monarchy of the United Kingdom, King of the United Kingdom, and the British Dominions, Emperor of India
*
H. H. Asquith – Prime Minister of the United Kingdom (until 5 December 1916)
* David Lloyd George – Prime Minister of the United Kingdom (from 7 December 1916)
* Field marshal (United Kingdom), Field Marshal Herbert Kitchener, 1st Earl Kitchener, Horatio Herbert Kitchener – Secretary of State for War (5 August 1914 – 5 June 1916)
* Edward Stanley, 17th Earl of Derby – Secretary of State for War (1916– )
* General (United Kingdom), General Sir William Robertson, 1st Baronet, William Robertson – Chief of the General Staff (United Kingdom), Chief of the Imperial General Staff (23 December 1915 – February 1918)
* General Sir Henry Wilson, 1st Baronet, Henry Wilson – Chief of the Imperial General Staff (February 1918 – February 1922)
* Field Marshal John French, 1st Earl of Ypres, John French – Commander-in-Chief of the
British Expeditionary Force (4 August 1914 – 15 December 1915)
* General/Field Marshal
Douglas Haig
Field marshal (United Kingdom), Field Marshal Douglas Haig, 1st Earl Haig (; 19 June 1861 – 29 January 1928) was a senior Officer (armed forces), officer of the British Army. During the First World War he commanded the British Expeditionary F ...
– Commander-in-Chief of the British Expeditionary Force (15 December 1915 – 11 November 1918)
* General David Henderson (British Army officer), Sir David Henderson – Director-General of Military Aeronautics
* General Hugh Trenchard, 1st Viscount Trenchard, Hugh Trenchard – Commander of the Royal Flying Corps – (August 1915 – January 1918) and Chief of the Air Staff (United Kingdom), Chief of the Air Staff of the combined
Royal Air Force
The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
– 1 April 1918 – 13 April 1918
* Brigadier (United Kingdom)#Historical rank of brigadier general, Brigadier General Sir Frederick Sykes – Chief of the Air Staff (United Kingdom), Chief of the Air Staff – 13 April 1918 through 11 November 1918 (post-war to 31 March 1919)
* Winston Churchill – First Lord of the Admiralty – (1911 – May 1915)
* Arthur Balfour- First Lord of the Admiralty – (May 1915 – December 1916)
* Edward Carson – First Lord of the Admiralty – (10 December 1916 – 17 July 1917)
* Eric Geddes – First Lord of the Admiralty – (July 1917 – January 1919)
* Admiral of the Fleet (Royal Navy), Admiral of the Fleet John Fisher, 1st Baron Fisher, John "Jackie" Fisher – First Sea Lord and Chief of the Naval Staff, First Sea Lord – (1914 – May 1915)
* Admiral (Royal Navy), Admiral Henry Jackson (Royal Navy officer), Henry Jackson – First Sea Lord – (May 1915 – November 1916)
* Admiral John Jellicoe, 1st Earl Jellicoe, John Jellicoe – Commander of the Grand Fleet (August 1914 – November 1916); First Sea Lord (November 1916 – December 1917)
* Admiral Rosslyn Wemyss, 1st Baron Wester Wemyss, Rosslyn Wemyss – First Sea Lord (December 1917 – November 1919)
* Admiral David Beatty, 1st Earl Beatty, David Beatty – Commander of the Grand Fleet (November 1916 – April 1919)
* General Archibald Murray – Commander of the Egyptian Expeditionary Force (January 1916 – June 1917)
* General
Edmund Allenby – Commander of the Egyptian Expeditionary Force (June 1917 – November 1918)
* Eric John Eagles Swayne – Commander of British forces in the Somaliland campaign, Somaliland Campaign
* William Peyton – commander and military secretary to the British Expeditionary Force
* Colonel (United Kingdom), Colonel T. E. Lawrence – a main leader of the
Arab Revolt
Dominion of Canada
* Robert Borden – Prime Minister of Canada (1914–18)
* Sam Hughes – Minister of Militia and Defence (1914 – January 1915)
* Joseph Flavelle – Chairman of the Imperial Munitions Board (1915–19)
* Lieutenant-general (United Kingdom), Lieutenant-General Edwin Alderson – Commander of the unified
Canadian Corps
The Canadian Corps was a World War I corps formed from the Canadian Expeditionary Force in September 1915 after the arrival of the 2nd Canadian Division in France. The corps was expanded by the addition of the 3rd Canadian Division in December 19 ...
of the Canadian Expeditionary Force (26 January 1915 – September 1915)
* General (United Kingdom), General Julian Byng, 1st Viscount Byng of Vimy, Julian Byng – Commander of the unified Canadian Corps of the Canadian Expeditionary Force (June 1916 – June 1917)
* General (Canada), General
Arthur Currie – Commander of the unified Canadian Corps of the Canadian Expeditionary Force (June 1917 – August 1919)
[first Canadian to attain the rank of full general]
Commonwealth of Australia
* Joseph Cook – Prime Minister of Australia (until 17 September 1914)
* Andrew Fisher – Prime Minister of Australia (17 September 1914 – 27 October 1915)
* Billy Hughes – Prime Minister of Australia (from 27 October 1915)
* General (United Kingdom), General William Birdwood – Commander of the
Australian Corps (all five Australian infantry divisions serving on the Western Front) (November 1917 – May 1918)
* Lieutenant general (Australia), Lieutenant General Sir
John Monash
General (Australia), General Sir John Monash (; 27 June 1865 – 8 October 1931) was an Australian civil engineer and military commander of the World War I, First World War. He commanded the 13th Brigade (Australia), 13th Infantry Brigade befor ...
– Commander of the
Australian Corps (May 1918 –)
* Major general (Australia), Major General William Holmes (Australian general), William Holmes – Commander of the Australian Naval and Military Expeditionary Force (August 1914 – February 1915)
* Lieutenant General Sir Harry Chauvel – Commander of the Desert Mounted Corps (Sinai and Palestine) (August 1917 –)
British India
* Charles Hardinge, 1st Baron Hardinge of Penshurst – Governor-General of India, Viceroy of India (1910–1916)
* Frederic Thesiger, 1st Viscount Chelmsford – Viceroy of India (1916–1921)
* Robert Crewe-Milnes, 1st Marquess of Crewe – Secretary of State for India (May 1911 – May 1915)
* Austen Chamberlain – Secretary of State for India (May 1915 – July 1917)
* Edwin Montagu, Edwin Samuel Montagu – Secretary of State for India (July 1917 – March 1922)
* Beauchamp Duff – Commander-in-Chief, India, Commander-in-Chief, India (March 1914 – October 1916)
* Sir Charles Monro, 1st Baronet, Charles Monro – Commander-in-Chief, India (October 1916 – November 1920)
* Lieutenant-general (United Kingdom), Lieutenant-General John Nixon (Indian Army officer), John Nixon – commander of the
British Indian Army (active in the Middle East)
Union of South Africa
* General (United Kingdom), General Louis Botha – Prime Minister of South Africa
* General Jan Smuts – led forces in the South West Africa campaign, South West Africa Campaign and East African campaign (World War I), East African Campaign, later a member of the
Imperial War Cabinet
Dominion of New Zealand
* William Massey – Prime Minister of New Zealand
* General Sir Alexander Godley – Commandant of New Zealand Military Forces (to October 1914); Commander of the New Zealand Expeditionary Forces
* Major General Sir Alfred Robin, Alfred William Robin – Quartermaster-General and Commandant of New Zealand Military Forces (from October 1914)
* Major General Sir Andrew Hamilton Russell – Commander of the New Zealand Division
Dominion of Newfoundland
* Edward Morris, 1st Baron Morris, Sir Edward Morris – List of premiers of Newfoundland and Labrador, Prime Minister of Newfoundland (1909–1917)
* John Chalker Crosbie, Sir John Crosbie – Prime Minister of Newfoundland (1917–1918)
* William F. Lloyd, Sir William Lloyd – Prime Minister of Newfoundland (1918–1919)
Japan
* Emperor Taishō – Emperor of Japan
* Ōkuma Shigenobu – Prime Minister of Japan (16 April 1914 – 9 October 1916)
* Terauchi Masatake – Prime Minister of Japan (9 October 1916 – 29 September 1918)
* Hara Takashi – Prime Minister of Japan (29 September 1918 – 4 November 1921)
* Katō Sadakichi – Commander-in-Chief of the 2nd Fleet (Imperial Japanese Navy), Second Fleet deployed to the Siege of Tsingtao
* Kōzō Satō – Commander of the Second Special Task Fleet
* Kamio Mitsuomi – Commander of Allied land forces Siege of Tsingtao, at Tsingtao
Italy (1915–1918)
* Victor Emmanuel III of Italy, Victor Emmanuel III – King of Italy
*
Antonio Salandra – Prime Minister of Italy, Prime Minister (until 18 June 1916)
* Paolo Boselli – Prime Minister (18 June 1916 – 29 October 1917)
* Vittorio Emanuele Orlando – Prime Minister (from 29 October 1917)
* Luigi Cadorna – Commander-in-Chief of the Royal Italian Army
* Armando Diaz – Chief of General Staff of the Royal Italian Army
* Prince Luigi Amedeo, Duke of the Abruzzi, Luigi, Duke of Abruzzi – Commander-in-Chief of the Adriatic Fleet of Italy (1914–17)
* Paolo Thaon di Revel – Admiral of the Regia Marina, Royal Italian Navy
Romania (1916–1918)
* Ferdinand I of Romania, Ferdinand I – King of Romania
* General Constantin Prezan – Chief of the General Staff of Romania
* Ion I. C. Brătianu – Prime Minister of Romania
* Vintilă Brătianu – Secretary of War
* Mareșal (Romania), Field Marshal Alexandru Averescu – Commander of the Second Army (Romania), 2nd Army, 3rd Army, then Army Group South
* General Eremia Grigorescu – Commander of the 1st Infantry Division (Romania), 1st Army
Portugal (1916–1918)
* Bernardino Machado – President of Portugal (until 12 December 1917)
* Afonso Costa – Prime Minister of Portugal (until 15 March 1916; then again 25 April 1917 – 10 December 1917)
* António José de Almeida – Prime Minister of Portugal (15 March 1916 – 25 April 1917)
* Sidónio Pais – Prime Minister of Portugal and War Minister (11 December 1917 – 9 May 1918) and President of Portugal (from 9 May 1918)
* José Norton de Matos – War Minister (until 10 December 1917)
* João Tamagnini Barbosa – Interim War Minister (9 May 1918 – 15 May 1918)
* Amílcar Mota – Secretary of State for War (15 May 1918 – 8 October 1918)
* Álvaro de Mendonça – Secretary of State for War (from 8 October 1918)
* Fernando Tamagnini de Abreu e Silva, Fernando Tamagnini de Abreu – Commander of the Portuguese Expeditionary Corps, Portuguese Expeditionary Corps (CEP)
* José Augusto Alves Roçadas – Commander of the Portuguese Forces in Southern Angola
* José Luís de Moura Mendes – Commander of the Portuguese Forces in Eastern Africa (until June 1916)
* José César Ferreira Gil – Commander of the Portuguese Forces in Eastern Africa (from June 1916)
* Sousa Rosa – Commander of the Portuguese Forces in Eastern Africa (from 1917)
Greece (1916/17–1918)

* Constantine I of Greece, Constantine I: King of Greece, he retired from the throne in June 1917, due to Allied pressure, without formally abdicating.
* Alexander of Greece, Alexander: King of Greece from 1917 after his father was forced into exile
*
Eleftherios Venizelos: Prime Minister of Greece after 13 June 1917
* Panagiotis Danglis: Greek general of the Hellenic Army
United States (1916–1918)

* Woodrow Wilson – President of the United States/Commander-In-Chief of the US Armed Forces
* Newton D. Baker – United States Secretary of War, US Secretary of War
* Josephus Daniels – United States Secretary of the Navy, US Secretary of the Navy
* Major general (United States), Major General/General (United States), General John J. Pershing – Commander of the American Expeditionary Forces
* Rear admiral (United States), Rear Admiral/Vice admiral (United States), Vice Admiral William Sims – Commander of United States Navy, US Naval Forces in European Waters
* Brigadier general (United States), Brigadier General Mason Patrick – Commander of the United States Army Air Service, US Army Air Service
Siam (1917–1918)
* Vajiravudh, King of Siam
* Chaophraya Bodindechanuchit (Arun Chatrakul), Chaophraya Bodindechanuchit, Ministry of Defence (Thailand), Minister of Defence
* Chakrabongse Bhuvanath, Supreme Commander of the Siamese Expeditionary Forces in
World War I
World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
* Phraya Thephatsadin, Commander of the Siamese Expeditionary Forces in the
Western Front
Brazil (1917–1918)
* Venceslau Brás – President of Brazil
* Pedro Max Fernando Frontin, Pedro Frontin, Chief of the ''Divisão Naval em Operações de Guerra'' (Naval Division in War Operations)
* José Pessoa Cavalcanti de Albuquerque, lieutenant of the Brazilian Army in France
* Napoleão Felipe Aché, Chief of Brazilian Military Mission in France (1918–1919)
* Doctor of Medicine, M.D. Nabuco Gouveia – Chief of Brazilian Military Medical Commission
Armenia (1917–1918)
* Hovhannes Kajaznuni – first Prime Minister of Armenia, Prime Minister of the First Republic of Armenia
* Andranik, General Andranik – military commander and statesman of the Caucasus campaign, Caucasus Campaign
* Aram Manukian – Minister of Internal Affairs of the First Republic of Armenia
* Drastamat Kanayan – military commander and member of the Armenian Revolutionary Federation
* Tovmas Nazarbekian – Commander-in-Chief of the First Republic of Armenia
* Movses Silikyan – army general and national hero
Czechoslovakia (1918)
* Tomáš Masaryk, Tomáš Garrigue Masaryk – first List of presidents of Czechoslovakia, President of First Czechoslovak Republic, Czechoslovakia
* Milan Rastislav Štefánik – Commander of the
Czechoslovak Legion
* Edvard Beneš – Ministry of Foreign Affairs (Czechoslovakia), Minister of Foreign Affairs and Ministry of the Interior (Czechoslovakia), the Interior
Personnel and casualties

These are estimates of the cumulative number of different personnel in uniform 1914–1918, including army, navy and auxiliary forces. At any one time, the various forces were much smaller. Only a fraction of them were frontline combat troops. The numbers do not reflect the length of time each country was involved.
See also
* Allied intervention in the Russian Civil War
* Causes of World War I
* Color books, transcripts of official documents released by each nation early in the war
* Diplomatic history of World War I
** British entry into World War I
** French entry into World War I
* Historiography of the causes of World War I
* Home front during World War I
** Belgium in World War I
** French Third Republic#First World War, France in World War I
** History of Germany during World War I, Germany in World War I
** Military history of Italy during World War I, Italy in World War I
** Romania during World War I, Romania in World War I
** History of the United Kingdom during World War I, United Kingdom in World War I
** United States home front during World War I, United States in World War I
** Japan during World War I, Japan in World War I
* International relations of the Great Powers (1814–1919)
* July Crisis
Footnotes
References
Bibliography
* Ellis, John and Mike Cox. ''The World War I Databook: The Essential Facts and Figures for All the Combatants'' (2002)
* Esposito, Vincent J. ''The West Point Atlas of American Wars: 1900–1918'' (1997); despite the title covers entire war
online maps from this atlas* Falls, Cyril. ''The Great War'' (1960), general military history
*
* Gooch, G. P. ''Recent Revelations of European Diplomacy'' (1940), 475pp; summarises memoirs of major participants
* Higham, Robin and Dennis E. Showalter, eds. ''Researching World War I: A Handbook'' (2003); historiography, stressing military themes
* Pope, Stephen and Wheal, Elizabeth-Anne, eds. ''The Macmillan Dictionary of the First World War'' (1995)
* Strachan, Hew. ''The First World War: Volume I: To Arms'' (2004)
* Trask, David F. ''The United States in the Supreme War Council: American War Aims and Inter-Allied Strategy, 1917–1918'' (1961)
*
* Tucker, Spencer, ed. ''The Encyclopedia of World War I: A Political, Social, and Military History'' (5 volumes) (2005); online at eBook.com
* United States. War Dept. General Staff. ''Strength and organisation of the armies of France, Germany, Austria, Russia, England, Italy, Mexico and Japan (showing conditions in July, 1914)'' (1916
online*
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{{DEFAULTSORT:Allies of World War I
Allies of World War I
1919 in law
20th-century military alliances
Aftermath of World War I
Military alliances involving Australia
Military alliances involving Canada
Military alliances involving France
Military alliances involving New Zealand
Military alliances involving South Africa
Military alliances involving the United Kingdom
Military alliances involving the United States
World War I by country
History of diplomacy