In my opinion Hitler's biggest mistake was attacking the USSR before he had defeated Britian. I was watching a movie about Stalin's life and during the war Stalin was content to leave Hitler alone because he thought that himself and Hitler could get along. However when Hitler attacked him I think he made a huge mistake the Soviet Union had one of the largest tank divisions in the world at that time. If Hitler had waited until after he had beat England he could have rebuilt his force and then fought the Russians 1 on 1 and the world would probally be quite a bit different now.