It should be a revelation because war is a civilizational concept - it's a form of organized violence, 'organization' being the keyword here.

If you're living in scattered, small tribes, then at most you can get into small tribal scuffles and vendetta ... but war requires planning, organization, support, possibly diplomacy, marshalling of resources - so it's hard to have proper war without the mechanisms in place to support it.

So maybe it's not quite so obvious.