Quote Originally Posted by Antagonist
It always seemed to me that either all alliances are completely insincere or the MTW AI uses assassins in a way which is completely unconnected from the diplomatic system, since I often find that everyone is out to get me with hired killers even if otherwise they seem to love me. It particularly bothered me that the Pope seemed to have it in for me, despite my attempts to behave as an exemplar of Christian monarchy...
I think part of the problem is that the A.I. does not realize that its assassins can get caught in your land and tries to send them by the shortest route. They need not necesarily be out for your skin. Also, it's a fool who doesn't gather information on allies as well as enemies.

On the other hand, in S:TW some faction were very reliable allies and some would stab you in the back just because they had nothing better to do. I presume it is the same in M:TW, only faction personalities change more often.