Some clues :
Douglas P. Fry : Pacified Past
Azar Gat : Warfare as an Ancient Feature
Robert Carneiro : Complexity and State Formation
Was the 20th century one of the most violent in human history ? (with two world wars and numerous other conflicts) ?
i also like the documentary series : “The Ascent of man” from the BBC in 1973 by Jacob Bronowski.
I feel like it has more to do with the technological advances than being more prone to conflict
Especially since Nagasaki there has been a disinclination to trigger the kind of mass destruction that will occur with such a conflict.