Stalin couldn’t have done it without the vast amounts of money the US sent his way (Russian nationalists don’t like to talk about Lend-Lease), and without the US and Western European countries fighting the Nazis on a second front.

Even then, Stalin’s psycopathy and ruthless incompetence caused far a far higher casualty rate than on the western front. He was fine throwing infantry into the meat grinder in a war of attrition, because Russia had more bodies than Germany did.