Combat in Civilization is the usual way in which a unit is destroyed. Combat outcomes are randomly determined and simple. Each unit's chance of winning is proportional to the relevant strength. For example, if a Veteran Battleship (attack strength 27) attacks a non-veteran Militia that's on a plain or desert (defensive strength 1), the Battleship has a 27/28 chance of winning. The loser disappears from the game. The winner stays where it is, unharmed; if it was the attacker and has movement points remaining, it can attack something else immediately.