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 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 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.
