Codominance

Choose two creature types among creatures on
the battlefield. Destroy all creatures that are not
of the chosen type. They can't be regenerated.
Two tribes desire heavily to go to war with one another, for the sake of honor and domestic pride. To make sure they have their war, they have signed an armistice. They have also agreed to lay waste to all
who oppose their grand war to finally end their slewing of insults that was never advancing their strife.