In High School, a friend had a shortwave radio. He listened to Radio Moscow to understand the sort of drivel they were putting out. On the 20th anniversary of VE Day, Radio Moscow had an essay contest on “Why the Soviet Union Was Able to Defeat Nazism”. My friend wrote back that the Soviet contribution was made possible by Lend-Lease and the United States providing a second front via the Normandy invasion. The propaganda ministry was apparently almost apoplectic and actually wrote him back to “correct” him.
Kinda like “O” going to Iowas to sell a bill that has already been turned into law. You just have to ask “why?” if the original premise is so sound.
Actually, the Soviet Union set off WW II with the Molotov-Ribbentrop pact, which gave National Socialist Germany a free hand to invade Poland, then western Europe. The USSR then collaborated in the rape of Poland. Stalin gloated over his "brilliance" in turning the Nazis loose on the western democracies.
Britain and France went to war to restore the independence to Poland, but the war ended with only Stalin really winning, because all of E. Europe plus much of Germany were then in the Soviet empire. In terms of long-term strategic consequences, the Nazis were effectively facilitators of Soviet interests.
I'll tell you what ended up defeating Nazism, Mussolini. Hitler had to pull Il Duce's chestnuts out of the fire in the Balkans, and it delayed Operation Barbarossa by a few critical months. Had the Germans stuck with the original plan, they would have been in Moscow before the harsh winter of '41.
Who ever heard of foreign troops participating in something like this?