Here's the deal. I'm playing as the Italians and decide I need to build up a little colony along the Baltic. Being that I'm all about the trade, I figure I'll go and bribe my way into possesion of Lithuania, and Sweden and just take over Livonia, Prussia and Norway when I need some more trade goods. You know... invest in my nation's future. Anyway 1109 I take control of Lithuania. 1110 Pesants go apeshit and I run like a little bitch for the castle. Figure at the very least I can hold out for a couple of years and bribe myself into command of on of the FOUR stacks of rebels and maybe fight my way out. Haven't got a line of ship's yet but working on it, so no reinforcement possibilty.
Well just so happens that I am allied with the Byzantines who are in control of Kiev. They decide to come in with a whole stack and help me lay waste to whole bunches of peons. Then they just go home... don't try invading me after or nothing. Like the AI was actually doing ...what... an ally... should. Weird, huh?