Hitler was a soldier in the German army. At the end of the war he, and many other German soldiers like him, could not get over the defeat of the German Empire. The German army command spread the myth that the army had not lost the war on the battlefield, but because they had been betrayed. By a ‘stab in the back’, as it was called at the time. Hitler bought into the myth: Jews and communists had betrayed the country and brought a left-wing government to power that had wanted to throw in the towel.
"Sumerian city-states fought each other" would be the best option from the list, since this internal division led to a collapse of power that left people without protection or a solid economy.
