You don't need war to have violence.

And we have plenty of evidence of violence from skeletons in various times going way back through the evolution of hominids.

For instance, 350kya: https://arstechnica.com/science/2022/02/early-humans-kept-getting-their-heads-knocked-in/

Or 1.8Mya: https://www.sciencedirect.com/science/article/pii/S0047248422000409

So I don't think your premise is all that sound.

Anyway, what is the modern rate of violence, compared to, say, 20kya or 350kya or 1.8Mya? Don't you think you would need to know something like that pretty well before you can make any argument in any direction?

Also, do you think it's relevant that "twentieth century hunter-gatherer societies are peaceful, egalitarian, and cooperative" when any aggressive hunter-gatherer society would have been obliterated by their angry much-more-populous neighbors ages ago (and at contact in modern times expressed a wider range of inequalities, e.g. https://www.pnas.org/doi/10.1073/pnas.2016134118)? In places with very limited contact with neighbors, like the Andaman Islands and the more remote reaches of Brazil, there can be great willingness to use violence against outsiders. (Again, partly selected for, because when it's so remote and the people are hostile, why not just leave them alone?)

Anyway, who is making the case that you're arguing against? I've literally never heard it anywhere, though I confess that the amount of right-wing media I consume to stay informed is rather modest, so it's plausible that I missed something there. And I ignore people like Andrew Tate--is this his kind of thing?