Conquering is the way to get another Castle. The very first step you should take in order to Conquer a Castle is to send your Army (with Noblemen included) on Attack march to the chosen target coordinates.
The Conquering of a Castle is possible only when the Attacker fulfills the following conditions:
- the Attacker must be the winner in the Battle;
- the Attacker must have alive Noblemen after the Battle;
- the Attacker must decrease Defender's Loyalty to 0.
- The level of the player's Order must allow more castles to be acquired.
Note that if your target has been declared Capital or it is the only Castle the player owns, you will not be able to Conquer it. So be careful when you send your Noblemen to take part in the Battle and protect yourself from losing them for nothing.
When you manage to Conquer a Castle, its Loyalty becomes 3000 and all marches on route to this castle are automatically returned.