This is a suggestion to have an event for provinces such as The Twins, Moat Cailin, and The Bloody Gate. The lord of these lands should be able to choose to not allow military units to pass through the province without a siege taking place. This is because the only way to get past these castles is to go through them and it is a bit annoying when an enemy can take 20k troops through the Bloody Gate without a fight and isn't forced to breach the gate.