Anthropology

Jane Goodall documented warfare between troops of chimps that was brutal. One side would not just conquer the other side; they exterminated them down to the last chimp infant. Generally, as far as she could tell, those wars were based on territorialism and resources. Looks like a trait that we share with our closest primate relatives.

AFAIK, chimps do not have theological bases for tgeir wars. At least we humans usually do not kill off all of the enemy. We conquer them, take their territory and resources, intermarry with conquered people, or enslave them. But once in a while, there are human throwbacks to our ancient genes, who try to kill off everyone who is "the other. "