Violence breeds violence and if the White Death Army is victorious, they will be the new threat like AD. If AD is victorious, they will turn around and burn all of your villages and settlements to the ground. This will just spawn more alliances and factions in a crusade to kill the other.
To quote Apocalypse Now: "There are two of you, don't you see? One that kills... and one that loves."
Be the one that loves.