I think if we're being real about it, the Soviets would have been able to beat the Nazis without help from anyone else. Maybe it's controversial, I don't know, but I think they could have done so, even without D-Day. Yes, we helped the Soviets with lend lease and occupying a a good number of Nazi troops with our not so secret plans of invasion. But after a couple of winters at Moscow and particularly the loss of the 6th army at Stallngrad, and then piling on with the failed offensive at Kursk, I think it's safe to say by mid 1943, there was nothing the Germans could have done to stop their defeat at the hands of the Soviets.