Comment by TheOtherHobbes

You're confusing interpersonal murder with tribal conflict.

Personal murder is tightly controlled now. But this is a fairly recent development. In many periods it was tolerated under various forms, including slavery, blood feud, honour killings, and state-sanctioned murder as punishment, or political process.

It's only in the last few centuries that it's been prohibited, and the prohibition in practice is still partial in many countries. (See also, gun control.)

Tribal murder has been the norm for most of recorded history. There are very, very few periods in very, very few cultures where there was no tribal/factional murder in living memory, and far more where it was an expected occurrence.

And technology has always been close by. Throughout history, most tech has either been invented for military ends or significantly developed and refined for them.