What do you mean by "early"? If you are talking 30,000 years ago or 6 thousand years ago, you're talking about two entirely different paradigms. I'll refer you to my story on the subject for more. There is no archeological evidence of war or mass killing before 13k years ago.
https://medium.com/inside-of-elle-beau/war-wasnt-in-our-ancestor-s-best-interests-63990c8417a7