The Characteristics of the Second World War

Did Stalin set the allies back when he joined? Or is this overstated as a set of factors? I like it as a starting point to talk about these giants of that conflict. It's a huge question, but I think the personalities, the characters of each of them were absolutely central to the outcome of the war. Adolf Hitler was pretty much alone in any of the likely decision-makers of the German side to come up with the idea of invading Russia and then declaring war against an uninvatable country like America. With Stalin, you see a very interesting way from moving after Operation Barbarossa, after June 1941, where he loses three and a half million men in the first six