Attacking with Armies
An army can attack another army, a castle town or any building on the map. Buildings will be raided and damaged, but cannot be occupied or garrisoned. An attack on a castle town will result in a siege taking place. If the target is further away than your army's movement extent will allow, it will take more than one turn to reach it and launch an attack. Once an army has reached its target the battle panel will be displayed, prompting you to fight on the battlefield, resolve the battle automatically, withdraw or lay siege (when appropriate).
Sieges
In order to gain control of a garrisoned and fortified castle town it is often necessary to lay siege. During a siege your troops surround the castle town and can either attempt to starve the defenders into capitulation or launch a direct assault. The besieged force may also choose to sally out to meet you on the battlefield, but be aware that defeating them will not automatically result in the surrender of the castle to you. Victory in a siege turns ownership of the province over to your clan. You then have the option to occupy peacefully or loot the castle town. Looting provides a cash lump sum but carries a greater penalty to public order than occupation alone. There will also be public order issues if the new owners of a province are of a different religion to that of the populace.
Ambushes
An army positioned in a forest can sometimes launch an ambush against a passing enemy. If you choose to attack the opposing force will be deployed in marching, rather than battle, order. If you decide not to launch an ambush, the army will pass without being alerted to your presence. NB - If you are playing battles on hard or very hard difficulty and are ambushed it will not be possible to issue orders when the battle is paused.