Correction: Hitler was done in April of 1941 when he decided to invade Russia over the objections of all his generals. Hitler never came close to Moscow. By September of 1941 the Germans were still in their summer gear when it started snowing. The Russians kept pulling back knowing the Germans would soon be sitting ducks as they became bogged down in the tundra mud. Even the mighty German tanks had the wrong tracks for mud. The U.S. had no business getting involved in this conflict but FDR wanted in so he provoked the Japanese by cutting off their oil from Indonesia and funding the Flying Tigers from China among other things.