You do know that the USSR signed a trade deal with Nazi Germany even in 1940, right? When the rest of the world was already blockading Nazi Germany for... being Nazi's. In fact, in 1940 the Soviet Union delivered about 75% of Nazi Germany's imports, mostly in oil & steel. Stalin could've joined that blockade, and not supplied the necessary materials for the Nazi war machine -- but he didn't.

You can acknowledge that, and still acknowledge the USSR took the brunt of the force fighting the Nazi's. It's not a sports game, you don't have to pick sides.