chaos: I suppose you can counter-attack, and what I mean by that is, invade during the time they are attacking an ally.

Rubedo: But you have to keep in mind they might be on Eizon more frequently to check up on their invasion, so they could easily defend against your war, and then, take a piece of your nation (according to the rules). So I doubt it would really work, and it would be unfair for you to just "step in" and stop the war they are doing just like that. You can try, I suppose, though.