Tower defense

Tower defense is a subgenre of real-time strategy computer games.

The goal is to try to stop enemies from crossing the map by building towers which shoot at them as they pass. Enemies and towers usually have varied abilities and costs. When an enemy is defeated, the player earns money or points, which are used to buy or upgrade towers.

The choice and positioning of the towers is the essential strategy of the game. Many games, such as Flash Element Tower Defense, feature enemies that run 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 are a hybrid of these two types, with preset paths that can be modified to some extent by tower placement.

History
Tower Defense games began in 1990 when Atari Games released Rampart. Early tower defense games later began to appear post-1997 in minigames for other platforms, such as Final Fantasy VII. By 2000, maps for StarCraft, Age of Empires II, and WarCraft III were following suit. The first standalone tower defense game for PC was "Master of Defense", released on November 7th of 2005.

Eventually, independent game developers began using Adobe Flash to make stand-alone tower defense browser games, which led to the release of Flash Element Tower Defense in January 2007 and then Desktop Tower Defense in March of the same year. Desktop Tower Defense became immensely popular and earned an Independent Games Festival award, and its success led to a version created for the mobile phone by a different developer. Several other tower defense computer games achieved a level of fame, including Protector, Immortal Defense, GemCraft, and Plants vs. Zombies.

By 2008, the genre's success led to tower defense games on video game consoles such as Defense Grid: The Awakening on the PC and Xbox 360, and PixelJunk Monsters and Savage Moon for the PlayStation 3. Tower defense games have also appeared on handheld game consoles such as Lock's Quest and Ninjatown on the Nintendo DS, and there are dozens of games for the iPhone/iPod Touch and Android.

In November 2010, the genre was first brought to the blind gaming community with the release of Aprone's Towers of War.

Gameplay
Tower defense games are characterised by the positioning of static units by the player to defend against mobile enemy units who are trying to get from a start point to an end point. There is a set number of enemy units (or 'damage' the player can take from units reaching the end point) who can reach the end point before the level is lost. Some games use a static route that the enemy units follow around which the player places their towers, while others favour a free-form environment that allows the user to define the path the enemy units take. Some games use a mixture of both. Most games allow the upgrading of the player's towers.

Often an essential strategy is "mazing", which is the tactic of creating a long, windy path of towers 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.

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 units at all.

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 has been reported to start enforcing the trademark; specifically on the iPhone/iPod Touch platform as a number of small or independent developers are now receiving messages from Apple citing trademark violation:

Additionally, your application appears to contain features, namely a trademark name, that appears to infringe on rights owned by Com2us corporations, specifically TowerDefense.

Please remember that pursuant to your agreement with Apple, you represent and warrant that your application does not infringe the rights of another party, and that you are responsible for any liability to Apple because of a claim that your application infringes another party's rights. Moreover, we may reject or remove your application for any reason, in our sole discretion.

Upon resubmission of your application, please provide documentary evidence that you have the rights to use this content to ensure compliance with the iPhone Developer Program License Agreement at the time you resubmit your new binary to iTunes Connect.