The tactic of sending a large army through an enemy's homelands purely to raid and destory his troop building capabilities is a really gamey thing to do. Instead......invade and garrison newly captured castles with very small units, under 10 men if poss. Dont pillage cos it's gamey.
Now the AI needs to recapture the castle and seige times will be extreme.....so the AI will probably assault the castle and your 10 man unit can stand and watch as hundreds of em get taken out by the castle defences. Dont auto resolve whatever you do cos you'll lose and the enemy will only take minor casualties.
I've seen 500 man armies destroyed trying to take a citadel from a mere 5 CMAA. You can hold out for years sometimes but eventually the AI will recapture. Of course if you play to win then this wont seem like a cool tactic.....but if you play just for the love of the game and try to roleplay like I do.......
