Tower defense (TD) is a
subgenre
Genre () is any style or form of communication in any mode (written, spoken, digital, artistic, etc.) with socially agreed-upon conventions developed over time. In popular usage, it normally describes a category of literature, music, or other for ...
of
strategy games
A strategy game or strategic game is a game in which the players' uncoerced, and often autonomous, decision-making skills have a high significance in determining the outcome. Almost all strategy games require internal decision tree-style thinki ...
where the goal is to defend a player's territories or possessions by obstructing the enemy attackers or by stopping enemies from reaching the exits, usually achieved by placing defensive structures on or along their path of attack.
["Best Tower Defense Games of All Time. Damon Reece. April 27, 2015 ] This typically means building a variety of different structures that serve to automatically block, impede, attack or destroy enemies. Tower defense is seen as a subgenre of
real-time strategy
Real-time strategy (RTS) is a Video game genre, subgenre of strategy video games that does not progress incrementally in turn-based game, turns, but allow all players to play simultaneously, in "real time." By contrast, in Turn-based strategy, tur ...
video game
A video game or computer game is an electronic game that involves interaction with a user interface or input device (such as a joystick, game controller, controller, computer keyboard, keyboard, or motion sensing device) to generate visual fe ...
s, due to its real-time origins, even though many modern tower defense games include aspects of
turn-based strategy
Strategy video game is a major video game genre that focuses on analyzing and strategizing over direct quick reaction in order to secure success.
Although many types of video games can contain strategic elements, the strategy genre is most commo ...
. Strategic choice and positioning of defensive elements is an essential strategy of the genre.
History
Precursors
The tower defense genre can trace its lineage back to the
golden age of arcade video games
The golden age of arcade video games was the period of rapid growth, technological development, and cultural influence of arcade video games from the late 1970s to the early 1980s. The release of ''Space Invaders'' in 1978 led to a wave of shoo ...
in the 1980s. The object of the arcade game ''
Space Invaders
is a 1978 shoot 'em up video game developed and published by Taito for Arcade video game, arcades. It was released in Japan in April 1978, with the game being released by Midway Manufacturing overseas. ''Space Invaders'' was the first fixed s ...
,'' released in 1978, was to defend the player's territory (represented by the bottom of the screen) against waves of incoming enemies. The game featured shields that could be used to strategically obstruct enemy attacks on the player and assist the player in defending their territory, though not to expressly protect the territory. The 1980 game ''
Missile Command'' changed that by giving shields a more strategic role. In the game, players could obstruct incoming missiles, and there were multiple attack paths in each attack wave.
[The Creation of Missile Command and the haunting of its creator Dave Theurer. Alex Rubens. August 15, 2013. ] Additionally, in ''Missile Command'', the sole target of the attackers is the base, not a specific player character.
While later arcade games like ''
Defender'' (1981) and ''
Choplifter'' (1982) lacked the strategy element of ''Missile Command'', they began a trend of games that shifted the primary objective to defending non-player items. In these games, defending non-players from waves of attackers is key to progressing.
Parker Brothers' 1982 title ''
Star Wars: The Empire Strikes Back'' for the Atari 2600 was one of the first
tie-in
A tie-in work is a work of fiction or other product based on a media property such as a film, video game, television series, board game, website, role-playing game or literary property. Tie-ins are authorized by the owners of the original proper ...
s to popularize the base defense style. The concept of waves of enemies attacking the base in single file (in this case
AT-ATs) proved a formula that was subsequently copied by many games as the shift from arcade to
PC gaming
A personal computer game, or abbreviated PC game, also known as a computer game, is a video game played on a personal computer (PC). The term ''PC game'' has been popularly used since the 1990s referring specifically to games on "Wintel" (Micr ...
began. Players were now able to choose from different methods of obstructing attackers' progress.
[ (reprinted in '']The Comics Journal
''The Comics Journal'', often abbreviated ''TCJ'', is an American magazine of news and criticism pertaining to comic books, comic strips and graphic novels. Known for its lengthy interviews with comic creators, pointed editorials and scathing r ...
''. No.85. Pg.108. October 1983. ; later reprints in Ellison collections ''Sleepless Nights in the Procrustean Bed'' (1984) and ''An Edge in My Voice'' (1985)). ''
Sorcerer's Apprentice'' for the
Atari 2600
The Atari 2600 is a home video game console developed and produced by Atari, Inc. Released in September 1977 as the Atari Video Computer System (Atari VCS), it popularized microprocessor-based hardware and games stored on swappable ROM cartridg ...
featured
Mickey Mouse
Mickey Mouse is an American cartoon character co-created in 1928 by Walt Disney and Ub Iwerks. The longtime icon and mascot of the Walt Disney Company, Mickey is an anthropomorphic mouse who typically wears red shorts, large shoes, and white ...
and was first published in 1983.
Nintendo's popular 1980s
Game & Watch
is a series of handheld electronic games developed by Nintendo. Designed by Gunpei Yokoi, the first game, ''Ball'' was released in 1980 and the original production run of the devices continued until 1991. The name Game & Watch reflects thei ...
handheld games featured many popular precursors. With their fixed sprite cells with binary states, games with waves of attackers following fixed paths were able to make use of the technical limitations of the platform yet proved simple and enjoyable to casual gamers. ''Vermin'' (1980), one of the first, tasked players with defending the garden (a theme followed by many later games) from relentless horde of moles. The following years saw a flood of similar titles, including ''Manhole'' (1981), ''Parachute'' (1981), and ''Popeye'' (1981). 1982 saw multiple titles with the primary object of protecting buildings from burning: ''Fire Attack'', ''Oil Panic'' and ''Mickey & Donald''. The later titles utilized multiple
articulating screen
An articulating screen is a built-in small electronic visual display which is not fixed, but rather can be repositioned using a hinge or pivot. The articulating screen is known under different other names such as flip-out screen, flip screen, adju ...
s to increase the difficulty for players. With two screens these games introduced basic resource management (e.g. oil and water), forcing players to multitask. ''Green House'' (1982) was another popular two screen game in which players use clouds of pesticide spray to protect flowers from waves of attacking insects. Despite the early rush of archetypal titles, ultimately there was a general decline in fixed-cell games, due to their technical limitations, simplistic gameplay, and the rise of personal computers and handhelds the
Game Boy
The is a handheld game console developed by Nintendo, launched in the Japanese home market on April 21, 1989, followed by North America later that year and other territories from 1990 onwards. Following the success of the Game & Watch single-ga ...
; correspondingly, this genre also declined. A rare exception was ''Safebuster'' (1988 multi-screen) in which the player protects a safe from a thief trying to blow it up.
By the mid-1980s, the strategy elements began to further evolve. Early PC gaming examples include the 1984 Commodore 64 titles ''Gandalf the Sorcerer'', a shooter with tower defense elements, and
Imagine Software's 1984 release ''
Pedro''. ''Pedro'', a garden defense game, introduced new gameplay elements, including different enemy types as well as the ability to place fixed obstructions, and to build and repair the player's territory.
Modern genre emerges
''
Rampart
Rampart may refer to:
* Rampart (fortification), a defensive wall or bank around a castle, fort or settlement
Rampart may also refer to:
* LAPD Rampart Division, a division of the Los Angeles Police Department
** Rampart scandal, a blanket ter ...
'', released in 1990, is generally considered to have established the prototypical tower defense.
''Rampart'' introduced player-placed defenses and has distinct phases of build, defend and repair. These are now staple gameplay elements of many games in the genre. It was also one of the first
multiplayer video game
A multiplayer video game is a video game in which more than one person can play in the same game environment at the same time, either locally on the same computing system (couch co-op), on different computing systems via a local area network, or ...
s of its kind.
While ''Rampart'' was popular, similar games were rarely seen until the widespread adoption of the
computer mouse
A computer mouse (plural mice; also mouses) is a hand-held pointing device that detects Plane (mathematics), two-dimensional motion relative to a surface. This motion is typically translated into the motion of the Cursor (user interface)#Po ...
on the PC. The DOS title ''
Ambush at Sorinor'' (1993) was a rare exception from this era.
Tower defense gameplay also made an appearance on consoles with several
minigame
A minigame (also spelled mini game and mini-game, sometimes called a subgame or microgame) is a short game often contained within another video game. A minigame contains different gameplay elements and is often smaller or more simplistic than th ...
s in the ''
Final Fantasy
is a Japanese fantasy Anthology series, anthology media franchise created by Hironobu Sakaguchi which is owned, developed, and published by Square Enix (formerly Square (video game company), Square). The franchise centers on a series of fanta ...
'' series, including a tower-defense minigame in ''
Final Fantasy VI
also known as ''Final Fantasy III'' in its initial North American release, is a 1994 role-playing video game developed and published by Square for the Super Nintendo Entertainment System. It is the sixth main entry in the ''Final Fantasy'' ser ...
'' (1994) and the ''Fort Condor'' minigame in ''
Final Fantasy VII
is a 1997 role-playing video game developed by Square for the PlayStation. The seventh main installment in the ''Final Fantasy'' series, it was released in Japan by Square and internationally by Sony Computer Entertainment, becoming the first ...
'' (1997), which was also one of the first to feature
3D graphics
3D computer graphics, sometimes called CGI, 3D-CGI or three-dimensional computer graphics, are graphics that use a three-dimensional representation of geometric data (often Cartesian) that is stored in the computer for the purposes of perfor ...
. ''
Attack of the Mutant Penguins'' for the Atari Jaguar and MS-DOS was released in 1995. ''
Dungeon Keeper
''Dungeon Keeper'' is a strategy video game developed by Bullfrog Productions and released by Electronic Arts in June 1997 for MS-DOS and Windows 95. In ''Dungeon Keeper'', the player builds and manages a dungeon, protecting it from invading ' ...
'' (1997) had players defend the Dungeon Heart, a gigantic gem at the centre of your dungeon, which, if destroyed, would cause the player to lose the game.
''
Fortress
A fortification (also called a fort, fortress, fastness, or stronghold) is a military construction designed for the defense of territories in warfare, and is used to establish rule in a region during peacetime. The term is derived from L ...
'' was released for the
Game Boy Advance
The (GBA) is a 32-bit handheld game console, manufactured by Nintendo, which was released in Japan on March 21, 2001, and to international markets that June. It was later released in mainland China in 2004, under the name iQue Game Boy Advanc ...
in 2001.
As
real-time strategy
Real-time strategy (RTS) is a Video game genre, subgenre of strategy video games that does not progress incrementally in turn-based game, turns, but allow all players to play simultaneously, in "real time." By contrast, in Turn-based strategy, tur ...
games gained popularity in
PC gaming
A personal computer game, or abbreviated PC game, also known as a computer game, is a video game played on a personal computer (PC). The term ''PC game'' has been popularly used since the 1990s referring specifically to games on "Wintel" (Micr ...
, the easy proliferation of user-created scenarios on
Battle.net expanded the genre rapidly. Custom maps for ''
StarCraft: Brood War'' such as ''Turret Defense'' (May 2000) and ''Sunken Defense'' (November 2001) were early examples of the genre that retained popularity for decades. Both were released early in the game's lifecycle and had various versions evolve in parallel over time due to the open-source nature of maps.
''
Warcraft III
''Warcraft III: Reign of Chaos'' is a high fantasy real-time strategy computer video game developed and published by Blizzard Entertainment released in July 2002. It is the second sequel to '' Warcraft: Orcs & Humans'', after '' Warcraft II: Ti ...
'' (2002), another real-time strategy game capable of such scenarios, added
role-playing
Role-playing or roleplaying is the changing of one's behaviour to assume a role, either unconsciously to fill a social role, or consciously to act out an adopted role. While the ''Oxford English Dictionary'' offers a definition of role-playing ...
elements to them. The ''
Frozen Throne'' expansion (2003) included a secret tower-defense scenario in one of the official campaigns. Custom maps included ''Element TD'' and ''Gem Tower Defense'', from February 2006, which were initially created in ''
Warcraft III World Editor''.
2007–2008 boom
Between 2007 and 2008, the genre became a phenomenon, due in part to the popularity of the tower defense mode in real time strategy games, but mainly due to the rise of
Adobe Flash
Adobe Flash (formerly Macromedia Flash and FutureSplash) is a mostly discontinuedAlthough it is discontinued by Adobe Inc., for the Chinese market it is developed by Zhongcheng and for the international enterprise market it is developed by Ha ...
independent developers as well as the emergence of major
smartphone
A smartphone is a mobile phone with advanced computing capabilities. It typically has a touchscreen interface, allowing users to access a wide range of applications and services, such as web browsing, email, and social media, as well as multi ...
app store
An app store, also called an app marketplace or app catalog, is a type of digital distribution platform for computer software called applications, often in a mobile context. Apps provide a specific set of functions which, by definition, do not i ...
s from Apple and Google. The first stand-alone
browser game
A browser game is a video game that is played on the internet using a web browser. They are sometimes referred to more specifically by their format, such as Flash games or HTML5 games. They are generally free-to-play and can be either single-pl ...
s emerged in 2007.
Among them were the extremely popular titles ''
Flash Element Tower Defense'' released in January,
''
Desktop Tower Defense'' released in March
and ''Antbuster'' released in May.
''Desktop Tower Defense'' earned an
Independent Games Festival
The Independent Games Festival (IGF) is an annual festival at the Game Developers Conference (GDC), the largest annual gathering of the independent video game industry. Originally founded in 1998 to promote independent video game developers, ...
award, and its success led to a version created for the
mobile phone
A mobile phone or cell phone is a portable telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones ( landline phones). This rad ...
by a different developer.
Another significant Flash title released in 2008 was ''
GemCraft''.
Handheld game console
A handheld game console, or simply handheld console, is a small, portable self-contained video game console with a built-in screen, game controls and speakers. Handheld game consoles are smaller than home video game consoles and contain the con ...
were not ignored in the boom and titles included ''
Lock's Quest'' and ''
Ninjatown'' released in September and October respectively. ''
Bloons Tower Defense'' was first published in 2007, one of many in a series of balloon themed multi-platform games released.
The genre's success also led to new releases on PC and
video game console
A video game console is an electronic device that Input/output, outputs a video signal or image to display a video game that can typically be played with a game controller. These may be home video game console, home consoles, which are generally ...
s. Popular 2008 titles included ''
PixelJunk Monsters'' released in January, ''
Defense Grid: The Awakening''
and ''
Savage Moon'' in December.
Also released in 2008 were ''
geoDefense Swarm'', ''
geoDefense'', ''
GemCraft'', ''
Fieldrunners'', ''
Harvest: Massive Encounter'' and ''
Crystal Defenders''. ''
GauntNet'' was released in April 2009. ''
Plants vs. Zombies
''Plants vs. Zombies'' is a video game Media franchise, franchise developed by PopCap Games, a subsidiary of Electronic Arts (EA). The series follows the affiliates of David "Crazy Dave" Blazing as they use his plants to defend against a zombi ...
'' released in May 2009 was another highly popular tower defense which became a successful series on mobile devices. Also released that year were ''
Sentinel
Sentinel may refer to:
Places Mountains
* Mount Sentinel, a mountain next to the University of Montana in Missoula, Montana
* Sentinel Buttress, a volcanic crag on James Ross Island, Antarctica
* Sentinel Dome, a naturally occurring granit ...
'', ''
TowerMadness'', ''
Babel Rising'', ''
Creeper World'', ''
Sol Survivor'', ''
Comet Crash'', ''
Final Fantasy Crystal Chronicles: My Life as a Darklord'', ''
South Park Let's Go Tower Defense Play!'', ''
Starship Patrol'' and ''
Trenches
A trench is a type of excavation or depression in the ground that is generally deeper than it is wide (as opposed to a swale or a bar ditch), and narrow compared with its length (as opposed to a simple hole or pit).
In geology, trenches res ...
''.
With the arrival of Apple's
App Store
An app store, also called an app marketplace or app catalog, is a type of digital distribution platform for computer software called applications, often in a mobile context. Apps provide a specific set of functions which, by definition, do not i ...
tower defense developers adapted quickly to the touchscreen interface and the titles were among the most downloaded, many of them ported directly from Flash. ''
Kingdom Rush
''Kingdom Rush'' is a 2011 tower defense game developed by Ironhide Game Studio and published by Armor Games. In the game's medieval fantasy setting, players take control of a general serving under King Denas of Linirea, who must defend the lan ...
'', first released in 2011, sold more than seventeen million copies both on
App store
An app store, also called an app marketplace or app catalog, is a type of digital distribution platform for computer software called applications, often in a mobile context. Apps provide a specific set of functions which, by definition, do not i ...
and
Play store.
A new breed of 3D games

By the end of the boom, most tower defense games were still using side scrolling, isometric, or
top-down perspective
A variety of computer graphic techniques have been used to display video game content throughout the history of video games. The predominance of individual techniques have evolved over time, primarily due to hardware advances and restrictions ...
graphics. ''
Iron Grip: Warlord'', released in November, 2008 unsuccessfully pioneered the first person perspective shooter with the genre. The awkward combination of experimental tower defense mechanics with 3D graphics was not well received, but later titles refined its execution paving the way for a popular new breed of games. ''
Dungeon Defenders'', released in October 2010, was one of the first tower defense games to bring the genre to the
third person perspective. It sold over 250,000 copies in first two weeks of release and over 600,000 copies by the end of 2011. 2010 saw the release of ''
SteamWorld Tower Defense
''SteamWorld Tower Defense'' is a tower defense video game by Swedish video game developer Image & Form. It was released digitaIIy on Nintendo DSi in North America, Europe and Australia on July 5, 2010. It is the first game released in the ''Stea ...
'', ''
Protect Me Knight'', ''
The Tales of Bearsworth Manor'', ''
Revenge of the Titans'', ''
Arrow of Laputa
is a tower defense game developed and published by ArtePiazza in Japan on November 24, 2010 for the Nintendo DSi
The is a foldable dual-screen handheld game console released by Nintendo. The console launched in Japan on November 1, 200 ...
'', ''
Toy Soldiers
A toy soldier is a miniature figurine that represents a soldier. The term applies to depictions of uniformed military personnel from all eras, and includes knights, cowboys, American Indians, pirates, samurai, and other subjects that involve c ...
'' and ''
Robocalypse: Beaver Defense''.
The 2011 title ''
Sanctum'', and
its 2013 sequel popularized the first person shooter hybrid that was pioneered by these earlier games. ''
Orcs Must Die!'' also integrated the FPS genre into a fully 3D environment and went to have several sequels. ''
Anomaly: Warzone Earth'' released in 2011 introduced a variation of gameplay which has been described as "reverse tower defense", "tower attack", and "tower offense". In the game, the player must attack the enemy bases protected by numerous defenses. Sequels and other games have since experimented further with both styles of tower defense. ''
Tiny Heroes'', ''
Army of Darkness: Defense'', ''
Iron Brigade
The Iron Brigade, also known as The Black Hats, Black Hat Brigade, Iron Brigade of the West, and originally King's Wisconsin Brigade was an infantry brigade in the Union Army of the Potomac during the American Civil War. Although it fought ent ...
'', ''
Rock of Ages'' and ''
Trenches 2'' were also released in 2011.
''
Defender's Quest'', ''
Bad Hotel'', ''
Toy Defense'', ''
Strikefleet Omega'', ''
Unstoppable Gorg'', ''
Defenders of Ardania'', ''
Orcs Must Die! 2'', ''
Fieldrunners 2'', ''
Dillon's Rolling Western
''Dillon's Rolling Western'', known in Japan as , is a downloadable video game developed by Vanpool (company), Vanpool and published by Nintendo for the Nintendo 3DS. It is the first game in the ''Dillon'' series. Released exclusively through the ...
'', ''
Oil Rush'' and ''
Elf Defense Eng'' all came out in 2012. Around this period the genre matured, gaining recognition as a distinct sub-genre of strategy games and returning in numerous upgraded versions. ''
Chain Chronicle'' and ''
CastleStorm'' were released in 2013. ''
Plants vs. Zombies 2'' came out and
Prime World: Defenders featured deck-building mechanics. 2014 saw a number of brand new titles including ''
Space Run'', ''
Dungeon of the Endless'', ''
Island Days'', ''Final Horizon'' and ''
The Battle Cats'' as well the return of ''
Age of Empires: Castle Siege'', ''
Defense Grid 2 and'' ''
TowerMadness 2''. ''
Deathtrap'' and ''
Krinkle Krusher'' were first published in 2015.
More recent titles in the genre include ''
Rock of Ages 2: Bigger & Boulder'' (2017), ''Tower Battles'' (2017) and ''
Orcs Must Die! Unchained'' (2017), ''
Dillon's Dead-Heat Breakers'' (2018), ''
Eden Rising: Supremacy'' (2018), ''
Aegis Defenders'' (2018), ''
Bloons TD 6'' (2018), ''
Arknights'' (2019), ''
Taur'' (2020), ''Element TD 2'' (2020), ''Buster's Tower Defense'' (2021), and ''Path to Nowhere'' (2022).
With the advent of
social networking service
A social networking service (SNS), or social networking site, is a type of online social media platform which people use to build social networks or social relationships with other people who share similar personal or career content, interest ...
applications, such as the
Facebook Platform
The Facebook Platform is the set of services, tools, and products provided by the social networking service Facebook for third-party software component, third-party developers to create their own application software, applications and services t ...
, tower defense has become a popular genre with titles such as ''Bloons TD'' and ''Plants vs. Zombies Adventures'' making the transition to turn-based play.
Recent releases include ''
Star Fox Guard
is a 2016 tower defense video game co-developed by Nintendo and PlatinumGames for the Wii U. The game was bundled as a separate disc for the first print edition of '' Star Fox Zero'' and as a digital download code on the Wii U eShop afterwa ...
'' and ''
McDroid'' which came out in 2016.
Gameplay
The basic gameplay elements of tower defense are:
* territories, possessions, domiciles, (collectively, the "base") that must be defended by the player or players
* waves of multiple incoming "enemies" that must be defended against
* placement of "tower" elements, such as towers, or obstructions along the path of attacking enemies
What distinguishes tower defense base defending games from other base defending games (such as ''Space Invaders'', or other games where bases are defended) is the player's ability to strategically place, construct or summon obstructive constructions and constructive obstructions in the path of attacking enemies.
In a tower defense, the player's main character is often invincible, as their primary objective is the survival of the base rather than the player.
Some features of modern tower defense:
* Player-placed obstructions that can damage or kill enemy attackers before they destroy the base
* Ability to repair obstructions
* Ability to upgrade obstructions
* Ability to repair upgrades to obstructions
* Some sort of currency with which to purchase upgrades and repairs, this can be time,
in-game currency
A virtual economy (or sometimes synthetic economy) is an emergent economy existing in a virtual world, usually exchanging virtual goods in the context of an online game, particularly in massively multiplayer online games (MMOs). People enter t ...
or experience points, such as being earned by the defeat of an attacking unit.
* Enemies capable of traversing multiple paths at once
* Each wave usually has a set number and types of enemies
* Unlock new maps and levels
* Tower that have the ability to move
Many modern tower defense games evolved from real-time to turn-based, cycling through distinct gameplay phases such as build, defend, repair, and celebrate.
Many games, such as ''
Flash Element Tower Defense'' feature enemies that scamper through a "maze", which allows the player to strategically place "towers" for optimal effectiveness.
However, some versions of the genre force the user to create the "maze" out of their own "towers", such as ''
Desktop Tower Defense''.
Some versions of the genre are a hybrid of these two types, with preset paths that can be modified to some extent by tower placement, or towers that can be modified by path placement, or modifications that can be placed by tower paths.
Often an essential strategy is "mazing", the tactic of creating a long, winding path of towers (or "maze") to lengthen the distance the enemies must traverse to get past the defense. Sometimes "juggling" is possible by alternating between barricading an exit on one side and then the other side to cause the enemies to path back and forth until they are defeated. Some games also allow players to modify the attack strategy used by towers to be able to defend for an even more tantalizingly reasonable price.
The degree of the player's control (or lack thereof) in such games also varies, from games where the player controls a unit within the game world, to games where the player has no direct control over units at all, or even no control over the game whatsoever.
A common theme in tower defense games to have occasional "air" units which ignore the layout of the board (i.e. maze paths or obstructions) and travel directly to the end destination, or enemies which prioritize different targets than their main destination.
Some tower defense games or custom maps also require the player to not only defend their own board but send out enemies to attack their opponents' game boards (or opponent-controlled areas of a common game board) in return. Such games are also known as tower wars game boards.
USPTO trademark
On June 3, 2008,
COM2US Corporation was awarded the trademark for the term "Tower Defense", filed on June 13, 2007 – serial number 3442002. The corporation started enforcing the trademark: in early 2010, developers of games on
Apple
An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...
's
App Store
An app store, also called an app marketplace or app catalog, is a type of digital distribution platform for computer software called applications, often in a mobile context. Apps provide a specific set of functions which, by definition, do not i ...
received messages requiring name changes for their games, citing trademark violation.
Adding the phrase "Tower Defense" (in capital letters) to the description of an app submission to iTunesConnect and the app store automatically triggers a warning that the submission is likely to be rejected for use of the term; however, writing the phrase in lower case is still acceptable as "tower defense" is a valid description of a game style.
References
{{Video game genre, state=expanded
Video game genres