Hmm... in glancing at your link I notice the infamous Pinker graph (which only includes data going back a few thousand years). There is no question that within that time period there was greater violence than there is in modern times, but it doesn't take into account the 97% of human history that preceded that - of which there is no evidence of wide-spread violence or war. The massacre at Jebel Sahaba, about 13,000 years ago is widely recognized as the first site of mass armed conflict. Most large scale violence is really only in the past 8k years.

https://en.wikipedia.org/wiki/Jebel_Sahaba

In my opinion, the rise of social systems based in patriarchal dominance hierarchies as well as increased population density (and other factors) is at the root of increased violence - not state vs. non-state societies because what we had for the vast majority of human history was both non-state societies as well as little violence.

“Many social arrangements impede war, such as cross-group ties of kinship and marriage; cooperation in hunting, agriculture or food sharing; flexibility in social arrangements that allow individuals to move to other groups; norms that value peace and stigmatize killing; and recognized means for conflict resolution. These mechanisms do not eliminate serious conflict, but they do channel it in ways that either prevent killing or keep it confined among a limited number of individuals.

People are people. They fight and sometimes kill. Humans have always had a capacity to make war if conditions and culture so dictate.

But those conditions and the warlike cultures they generate became common only over the past 10,000 years — and, in most places, much more recently than that. The high level of killing often reported in history, ethnography or later archaeology is contradicted in the earliest archaeological findings around the globe.” Scientific American