Hate to say it, but animals and insects are just as capable of killing and going to war. It's not just humans. Ever watch wasps attack a beehive? That's definitely on the level of war, if not a complete massacre. Nature can be pretty scary and cruel in many ways, and many species have no issue with killing even their own kind.

Given, the death and destruction is not even near to the level of nuclear warfare, but it's still present.