Some clues :

Douglas P. Fry : Pacified Past
Azar Gat : Warfare as an Ancient Feature
Robert L. 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.