Tower defense
Tower defense is a subgenre of strategy video game where the goal is to defend a player's territories or possessions by obstructing the enemy attackers, usually achieved by placing defensive structures on or along their path of attack. 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 video games, due to its real-time origins, though many modern tower defense games include aspects of turn-based strategy. Strategic choice and positioning of defensive elements is an essential strategy of the genre.
Ryan Clements of IGN attributes the popularity of such games to psychology and human vulnerability. Tower defense, according to Clements, "plays off of our need for security, ownership, and a desire to protect the people closest to us" arising from a need to create intrinsic value through "ownership over things", "personal space" and to "repel our fears and insecurities".
History
Precursors
The tower defense genre can trace its lineage back to the golden age of arcade video games in the 1980s. The object of the arcade game Space Invaders, released in 1978, was to defend the player's territory against waves of incoming enemies. The game featured shields which 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. Missile Command was also the first of its kind to make use of a pointing device, a trackball, enabling players to use a crosshair. The innovation was ahead of its time and anticipated the genre's later boom, which was paved by the wide adoption of the computer mouse. Additionally, in Missile Command, the sole target of the attackers is the base, not a specific player character. For these reasons, some regard it as the first true game in the genre.While later arcade games like Defender and Choplifter 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 for the Atari 2600 was one of the first tie-ins to popularize the base defense style. The concept of waves of enemies attacking the base in single file proved a formula that was subsequently copied by many games as the shift from arcade to PC gaming began. Players were now able to choose from different methods of obstructing attackers' progress.
Nintendo's popular 1980s Game & Watch hand held 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, one of the first, had players with defending the garden from relentless horde of moles. The following years saw a flood of similar titles, including Manhole, Parachute, and Popeye. 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 screens to increase the difficulty for players. With two screens these games introduced basic resource management, forcing players to multi-task. Green House 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; correspondingly, this genre also declined. A rare exception was Safebuster 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, released in 1990 is generally considered to have established the prototypical tower defense. Rampart introduced player placed defenses that automatically attack incoming enemies. In addition, it 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 games of its kind.While Rampart was popular, similar games were rarely seen until the widespread adoption of the computer mouse on the PC. The DOS title Ambush at Sorinor was a rare exception from this era. Tower defense gameplay also made an appearance on consoles with several minigames in the Final Fantasy series, including a tower-defense minigame in Final Fantasy VI and the Fort Condor minigame in Final Fantasy VII, which was also one of the first to feature 3D graphics. Dungeon Keeper 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. A central theme of the 3D first person shooter ' was to defend Energy Totems against hordes of attackers.
As real-time strategy games gained popularity in PC gaming, many introduced tower defense modes in their gameplay, particularly in multiplayer. In February 2006, the custom maps for ', and Gem Tower Defense, which were created in Warcraft III World Editor, almost single-handedly rekindled the genre. These titles would also bring role-playing elements to the genre for the first time.
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 independent developers as well as the emergence of major smartphone app stores from Apple and Google. The first stand-alone browser games 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 award, and its success led to a version created for the mobile phone by a different developer. Another significant Flash title released in 2008 was GemCraft. Handheld game console were not ignored in the boom and titles included Lock's Quest and Ninjatown released in September and October respectively.With the arrival of Apple's App Store tower defense developers adapted quickly to the touchscreen interface and the titles were among the most downloaded, many of them ported directly from Flash. Among the more notable include Kingdom Rush which sold more than seventeen million copies both on App store and Play store.
The genre's success also led to new releases on PC and video game consoles. Popular 2008 titles included PixelJunk Monsters released in January, and Savage Moon in December. GauntNet was released in April 2009. Plants vs. Zombies released in May 2009 was another highly popular tower defense which became a successful series on mobile devices.
A new breed of 3D games
By the end of the boom, most tower defense games were still stuck in the side scrolling, isometric, or top-down perspective graphical medium. ', 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. The 2011 title Sanctum, and its 2013 sequel popularized the first person shooter hybrid that was pioneered by these earlier games.' 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.
With the advent of social networking service applications, such as the Facebook Platform, 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.
Gameplay
The basic gameplay elements of tower defense are:- territories, possessions, domiciles, loved ones 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
In a tower defense, unlike the base, the player's main character is often invincible, as the primary object 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 the obstructions 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 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.
It is a common theme in tower defense games to have "air" units which do not pass through the layout of the maze, but rather fly over the towers directly to the end destination.
Some tower defense games or custom maps also require the player to send out enemies to their opponents' game boards respectively their controlled areas at a common game board. Such games are also known as tower wars game boards.