To expand your faction’s empire in Total War: Three Kingdoms you will need to take over other faction’s settlements, towns, and cities. This means marching an army to their door and then laying siege to them. While you can, should you choose, just attack straight away, a siege will reduce their numbers, and affect their morale, making any battle much easier.
The risk of a siege is that the faction you are attacking might be able to muster another army, and either attack you with it before you can finish the siege, or else lay in wait for you afterward, taking advantage of any losses you suffered during the battle itself.
Settlements will have a garrison, but there can also be armies within the settlement, so you want to be very careful that you have a stronger force than your enemy before you attack them.
How To Prepare For A Siege
To begin a siege, select your army, then right click on the settlement. A new menu will populate that contains some very important information. You will be able to see the forces in your army on the lower left, and the forces in the enemy army on the lower right. If they have a garrison, and a standing army in the settlement, you will be able to see two small circular portraits on the right-hand side.
A very important thing to note is a color code bar, just below the flags of both factions in the center of the screen. This bar will denote your perceived chances of victory, based on the total number, and strength, of characters and units that both sides have. A green bar denotes a strong chance of victory, while a red bar denotes possible defeat.
You will also see two buttons. Start Battle allows you to fight the battle yourself, while Delegate allows you to just auto-resolved the fight, which might be the preferred option for a battle that is largely a foregone conclusion.
Below that, you will see three symbols. The first denotes how many turns it takes to starve out the settlement. The second shows how many turns it will be before the defenders start to take attrition damage, while the last shows how many barricades the defenders have access to.
You can, if you wish, demand that the other faction surrender, in which case they will give up the settlement without a fight. This, in my experience, will only happen if the battle is truly a foregone conclusion. Some characters, if they harbor a lot of hate for you, will never surrender and would rather die fighting.