The game is a real-time strategy game in which an Alien hive, a clan of Predators and an elite squad of Colonial Marines fight each other in 21 single-player missions, 7 for each race. Unlike as in the most other real-time strategy games in Aliens versus Predator: Extinction the player (s) do not have to do any building and base construction. The game is strictly focused on unit management and combat. Each race has a distinct method of obtaining new troops. (wikipedia.org)