The Washington Post has a not very well done piece about how the Russians won the European war. The point of the article is correct.
The explication could use some improvements. Especially as the comments are a carnival of rightwing misinformation and fantasies.
So on the 70th anniversary of the end, let's go back to the beginnings.
In the 1930s, fascist armies were on the march in Manchuria and China, Spain, Abyssinia, Austria and Czechoslovakia. Communist armies were not. The systems were about equally inhuman, but one was actually destroying states and killing foreigners and one was not.
This insight explains why Churchill, a rabid antiBolshevik for decades, was eager to ally with the USSR against Germany and Italy. (He was also opposed to the expansion of fascist Japan, but judged it inexpedient to try fighting that war if he could avoid it, which he couldn't.)
Stalin was deathly afraid of Germany and tried to make a defensive alliance with Britain and France. He said he was ready to march to the aid of Czechoslovakia in 1938. The Czechs and Poles were suspicious, and we cannot know how that would have worked out for them. It probably would have finished Hitler, though, which would likely have been a net gain for people in general.
Stalin's desperation to keep the peace in central Europe was proved by his attempt to buy Karelia from Finland in order to strengthen the defenses around Leningrad. The Finns, like the Czechs and Poles, were not cooperative.
It was only when all his attempts to manufacture collective security systems were rejected that the USSR started taking military steps of its own, by invading Estonia, Latvia, Lithuania and Romania, and later Finland. It is noteworthy that no Red Army soldier ever stepped beyond the borders of tsarist Russia, with the exception of the "volunteers" in Spain.
Russia was committed to the integrity of the international state system, as proven by its scrupulous withdrawal to original borders after it repelled the invasion of the Japanese at Nomonhan, The fact is, Bolshevism was on the run by 1938-39. Communists by the hundreds of thousands had been murdered by fascists, notably in China and Spain, and there were only two Bolshevist states, the USSR and Mongolia.
In contrast, few fascists had been murdered by Bolsheviks and fascism was ascendant in most of Europe, much of Asia and parts of Africa.
The German-Soviet non-aggression treaty of August 1939 was Stalin's admission that his years of efforts to preserve peace had failed. Like the Czechs, he had run out of desirable choices in the face of endless fascist aggression.
Like the Poles, who had reacted to German aggression against Czechoslovakia by also invading Czechoslovakia, it was a bad move, fatal for Poland, nearly so for Russia.
Two things saved Russia. First, Britain refused to agree to Hitler's proposal for a new settlement of Europe following the collapse of France and kept the war going. Second, in April 1941, Serbian royalists overthrew the fascist government of Yugoslavia, forcing Hitler to invade the Balkans.
Like the policies of Czechoslovakia and Poland, the effort of the Serbs was suicidal, yet it made it possible for the USSR to survive. Hitler's invasion of Russia was delayed for weeks, and his army somewhat reduced by the diversions to the Balkans and Crete.
The Germans (and world opinion generally) expected the USSR to collapse without much of a fight when Germany invaded. It seems likely that many of the Russian Bolsheviks agreed.
One well-informed man warned that if Russia resisted, Germany could not win. This was General Georg Thomas, director of the economic warfare section of the German high command. He calculated that if the Russians inflicted a million casualties, the Germans would run out of men.
He was right. In September 1941, the millionth German casualty occurred. After that, the strength of the German army declined. If the Russians held steady, they would eventually prevail.
This is where the sacrifice of the Serbs becomes crucial. Although the German army was weakening, it still had enough power to (probably) take Moscow. Whether this would have finished the war is doubtful, but it is possible.
The Russians resisted without regard to their own losses, but they were being pushed back as long as the dry weather held. The autumn rains stopped the Germans in the suburbs of Moscow; the delay imposed by the Serbian rebels had bought just enough time.
There was immense destruction to come but it was meaningless; the outcome was decided.
The United States had nothing to do with it. Not a bullet or a bean had reached the Red Army. At the point when the outcome was decided, the only contribution of the Americans was to the naval war in the Atlantic.