When you declare War the cost depends on the Tier of War Camp you decide on.
Your options are:
1: Normal Gate Strength, Deployment Limit of 6, Normal Siege Supply Rate, 7,500 Gold
2: High Gate Strength, Deployment Limit of 8, High Siege Supply Rate, 10,000 Gold
3: Highest Gate Strength, Deployment Limit of 10, Highest Siege Supply Rate, 15,00 Gold
The Gate Strength refers to the War Camp gate's integrity or "health".
Deployment Limit refers to the amount of Siege Platforms that can be
deployed at any one time. Keep in mind that attacker Siege Platforms
can be picked up and moved around and will not count towards the
Deployment Limit if they are not on the battlefield. Siege Supply is a
resource generated at the Attackers' War Camp and Defenders' Fort used
to repair structures such as gates, as well as Siege Weapons.
If the attacking army prevails, they will now have control over the
Territory and everything within it. The defeated party will have lost
their Settlement and Fort, as well as all their Territorial Bonuses.
These can be earned back through another War declaration but the
Company would have to first regroup. After a War's conclusion, there
is a cooldown period before another War can be declared against that
Note: It costs nothing to the attackers afterwards to claim the territory. The only territory claim cost is on the initial company purchase of an unclaimed territory which costs 100,000 Gold.