In my lategame with 2 kingdoms left, the AI just took a string of castles and cities deep in our territory. I was thinking huh, if I take this one castle I can cut all of that off, except it doesn't work like that. I was thinking then, that castles should be given a role, and maybe mods will make it happen - make castles do something, that makes them necessary to take, if you want to proceed in that direction. You know like in real life lol. Maybe they should be blocking chokepoints, or harassing caravans or something. Right now there is no difference if a castle is right on the border or in the middle of enemy kingdom. It was like in that in warband as well, though it didn't seem so bad there, and these things could be developed further.