Rationalism led to the use of empiricism, or observation, in science. Francis Bacon invented the scientific method based on rationalism. It also lessened overbearing religious dogma
The Great Depression changed Germany politically by the formation of the Nazi party and the development of fascism or a complete dictatorship of the Germany's elite industrialists and they blamed the Jewish people on their economic problems thus deflecting criticism of bringing it on themselve ie the big industrialists. As for America entering the WWII, of course that was when the Japanese fascists attacked and burned Pearl Harbour thus forcing the US to respond and go to war.
The soviets lured the Germans farther into Russia, where Germany encountered massive supply shortages, as well as extremely cold weather they were unequipped to deal with
