There is evidence of war in the past 10,000 years, little before.

Prior to 500 years ago there was little modern contact with the Americas, Australia, parts of sub-Saharan Africa etc., so observation of lack of conflict in hunter-gatherer bands there is more evidence. Obviously I mean hunter-gatherers, not the Aztec warriors.

I don't see what chimpanzees have to do with humans, unless chimpanzees are sculpting Venus Madonnas and drawing buffalo on caves.