Additionally, in Missile Command, the sole target of the attackers is the base, not a specific player character. 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. Missile Command was also the first of its kind to make use of a pointing device, a trackball, enabling players to use a crosshair. In the game, players could obstruct incoming missiles, and there were multiple attack paths in each attack wave. The 1980 game Missile Command changed that by giving shields a more strategic role. 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 object of the arcade game Space Invaders, released in 1978, was to defend the player's territory (represented by the bottom of the screen) against waves of incoming enemies. The tower defense genre can trace its lineage back to the golden age of arcade video games in the 1980s. Strategic choice and positioning of defensive elements is an essential strategy of the genre.

Tower defense is seen as a subgenre of real-time strategy video games, due to its real-time origins, even though many modern tower defense games include aspects of turn-based strategy. This typically means building a variety of different structures that serve to automatically block, impede, attack or destroy enemies. Tower defense ( TD) is a subgenre of strategy games 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.

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