International law, also known as public international law and law of nations, is the set of rules, norms, and standards generally accepted in relations between nations. It establishes normative guidelines and a common conceptual framework to guide states across a broad range of domains, including war, diplomacy, trade, and human rights. International law aims at the practice of stable, consistent, and organized international relations.
The sources of international law include international custom (general state practice accepted as law), treaties, and general principles of law recognized by most national legal systems. International law may also be reflected in international comity, the practices and customs adopted by states to maintain good relations and mutual recognition, such as saluting the flag of a foreign ship or enforcing a foreign legal judgment.
International law differs from state-based legal systems in that it is primarily—though not exclusively—applicable to countries, rather than to individuals, and operates largely through consent, since there is no universally accepted authority to enforce it upon sovereign states. Consequently, states may choose to not abide by international law, and even to break a treaty. However, such violations, particularly of customary international law and peremptory norms (jus cogens), can be met with coercive action, ranging from military intervention to diplomatic and economic pressure.
The relationship and interaction between a national legal system (municipal law) and international law is complex and variable. National law may become international law when treaties permit national jurisdiction to supranational tribunals such as the European Court of Human Rights or the International Criminal Court. Treaties such as the Geneva Conventions may require national law to conform to treaty provisions. National laws or constitutions may also provide for the implementation or integration of international legal obligations into domestic law.
Hans Morgenthau believed international law to be the weakest and most primitive system of law enforcement; he likened its decentralised nature to the law that prevails in preliterate tribal societies. Monopoly on violence is what makes domestic law enforceable; but between nations, there are multiple competing sources of force. The confusion created by treaty laws, which resemble private contracts between persons, is mitigated only by the relatively small number of states. For example, it is unclear whether the Nuremberg trials created new law, or applied the existing law of the Kellogg-Briand pact.
Morgenthau asserts that no state may be compelled to submit a dispute to an international tribunal, making laws unenforceable and voluntary. International law is also unpoliced, lacking agencies for enforcement. He cites a 1947 US opinion poll in which 75% of respondents wanted "an international police to maintain world peace", but only 13% wanted that force to exceed the US armed forces. Later surveys have produced similar contradictory results.