With one or more combat units selected, right click on an enemy unit to attack it. How a unit attacks depends on their stance. Units in a battleline will attempt to hold their formation while engaging the enemy, while units in a skirmish stance will simply head towards the closest target. Units in a ranged stance will advance to within missile range and then begin firing on the enemy. See Stances for more information on how stances affect combat.
When units are sufficiently engaged in melee combat, they will become locked in combat and neither unit will be able to retreat until one or the other has been defeated.
A unit is defeated when all of its members are killed, or its morale is reduced to zero and the remaining members rout. Defeated units return to their home city to recruit new members.
When units run into combat they build up a charging bonus that may inflict extra damage at the moment of impact. The amount of the bonus is based on the unit's charging strength and speed as well as the blocking strength of the enemy.
Units that are being attacked from opposite sides receive a flanking penalty that continually drains morale as long as the unit is surrounded.
To capture units when they rout, try to position a unit in their flanks. You will have a better chance of getting them to surrender if they haven't engaged the enemy when they rout.
Using a ranged or melee ambush stance, units can remain undetected while within the enemy's normal view range. Units receive a significant ambush bonus if they attack an enemy without being sighted first. Ambush units are much harder to detect when they aren't moving, but once discovered they must move beyond the enemy's regular view range before they can ambush again.