The introduction of chariot warfare and large-scale "battlefield warfare".
Warfare didn't exist in that form; it was too early for his military model. Agricultural spread (7000 BC) Militarism and the Indo-Europeanizing of Europe
He dates the shift much later than the standard 4th–3rd millennium BC Kurgan model. complicating Drews' 1600 BC focus.
Modern ancient DNA studies increasingly support earlier, massive migrations from the Steppe during the Yamnaya period (c. 3000 BC), complicating Drews' 1600 BC focus. Militarism and the Indo-Europeanizing of Europe