You can put your army in various stances:
1. Marching-this is when your army is simply moving from one place to another
2. Offensive-this is when you are about to attack or are chasing an enemy. Attack of troops is increased although defensive abilities are decreased
3. Defensive-Your army will become entrenched at a certain defensive position. Movement is impossible although rudimentary defenses will be set up.
4. Guerilla-This sort of army will target the enemy supply lines, causing small casualties to the enemy. However, an outright attack is made impossible, and this can't be conducted on cities.
5. Fleeing-If your army has been defeated and you want to get out of enemy territory quickly then you can put your army on this setting. Speed is doubled although some units may get left behind and sacrificed if they are too slow, and the army will be strung out.