If you read The Bell Curve, they get into the various areas of functionality, tribalism, anthropology, intelligence, education, etc. They break it down ten ways to Sunday.
An interesting conclusion the book gets into is that the education is not very educational at all.
“but not end up with a continent-wide genocide.”
Actually, they did. All throughout the Americas there were genocidal wars. They weren’t bright enough to create new technologies but they sure used the ones they had with great prejudice.
Gotta agree that tribal warfare can be as savagely merciless (in intent, if not in extent) as anything developed by the civilized brutes of 20th century Europe.