Stopping a war short of full destruction requires both sides to agree to stop it. There are quite a few examples of this, where realms have refused to surrender. (Luz de Bia on BT is the first to come to mind, but there have been others.) This forces the other realm to kill them. Or the realms voluntarily suicide. (Caerwyn on Dwilight did this, taking their regions to Asylon rather than continue to exist as a smaller realm.)
It takes two hands to clap. That is why i always think rulers' interactions are very important to make their nobles enjoy the game/realm.
