One need only look at the pre-Columbian
Crow Creek Massacre to realize that the Native Americans didn't need Europeans to teach them how to kill, though the Moche of what is now Peru probably take the prize for most twisted and brutal in the Americas. Of course the ancestors of plenty of Europeans, Asians, and Africans were just as brutal. For example, read the content of the earliest Chinese writing in the form of Shang oracle bones. They did quite a bit of human sacrifice. The Celts had their own fair share, as well, especially if you assume the Romans were as honest as the Spaniards were.
