Let's not forget that humans evolved during dangerous times, and that survival of the individual/group often depended upon violent action -- from hunting for food to kill-or-be-killed. Within the group you did not kill, but you were wary of other groups -- offering the hand of friendship but with a firm grip on your knife or club. Sometimes, probably often, you got on well with the other group, but there were other times....

Then civilization arose and my city fought your city for whatever reason (and for a really stupid example of a reason read the Iliad - or the Old Testament).

The capacity for violence has been inbred for, literally, thousands of years. It might be a survival characteristic, I don't know. But I do know that if we don't learn to control it, and that very soon, it's going to kill us all.