One widely debated question is when Hitler first planned the Holocaust. Theories range from Lucy Dawidowicz's thesis that Hitler was planning the complete destruction of the Jews from 1919 onward but coding it in "dog whistle" language that only his most hardcore followers could understand to the theory of Christian Gerlach and other scholars who argue the decision was not made until December 12, 1941, as recorded in Nazi propaganda leader Goebbels's journal.
Another debated question is whether World War II could have been avoided if the League of Nations had moved against Hitler as soon as he began to aggressively claim territory in the mid 1930s. Could he have been stopped and disarmed (under the Versailles Treaty) before he became too powerful?
Historians also question what drove Nazi violence to such extreme levels? Theories range from overly strict parenting and discipline in German families to Klaus Theweleit in Male Fantasies who argues the Nazis simply attracted people who enjoyed violence.