If you read Jared Diamond or Stephen Pinker they talk about the really high levels of violence in the stone age.
Or to describe it with statistics
"By many estimates, 10 to 20 percent of all Stone Age humans died at the hands of other people.
This puts the past 100 years in perspective. Since 1914, we have endured world wars, genocides and government-sponsored famines, not to mention civil strife, riots and murders. Altogether, we have killed a staggering 100 million to 200 million of our own kind. But over the century, about 10 billion lives were lived — which means that just 1 to 2 percent of the world’s population died violently. Those lucky enough to be born in the 20th century were on average 10 times less likely to come to a grisly end than those born in the Stone Age. And since 2000, the United Nations tells us, the risk of violent death has fallen even further, to 0.7 percent."
To reduce violence don't send people back to the stone age.