I made this work just last nite: I was the Saxons in a VI Viking era campagin and allied with the Scots. They were attacked by the Pitcs and fortified themselves. I immedately attacked with a large force. The Pitcs decided that they couldn't win and withdrew. My forces were sent home by the AI and I got a nice thank you note from the Scotts saying that they would return the favor some time. I think that the key elements were the large force causing the Picts to withdraw and the fact that I went in while the provence was still in Scott hands.