Combat is initiated by one player attempting to move a stack onto a hex occupied by another player. If the players are at war, the attacker has the option of selecting tactical combat, where the players move individual units on a small map representing the battlefield, or automatic ("fast") combat, where the computer determines how the battle would have taken place by weighing off each side's attack, defense and movement parameters. Tactical combat is only available on single player maps, against independent units in PBEM games, and (optionally) against human players in live multiplayer games. Both forms of combat use the sequential turn system.