You speak about this as if it would be a bad thing. Awars are fun!
An alliance should exist for the sake of it's members, not for the sake of the alliance. Otherwise, what would be the point in joining.
You also speak of 1 v 1 kingdom situation as if you were speaking of equals.
The point of the alliance is to right injustice, not look the other way.
Is like saying that if in RL one of your buddies was getting hit you wouldn't get his back. You'd turn & walk away?