The unassailable fact is the Soviet people sustained terrible casualties during the war. And it is thanks to their resistance and tenacity that European fascism was later defeated. There's more:
The Soviet Union is not the only state to be written out of the victory story in the west. The Chinese people also lost an estimated 20 million as a result of Japanese aggression. Just as the Soviet armed forces held down the Germans, so the less effective but numerous Chinese armed forces kept the Japanese bogged down in Asia. This is a record that is still almost unknown in the west, yet if Japan had achieved quick victory in China, large resources would have been released for an assault on the rear of the Soviet Union, or a larger military presence in the Pacific. In this case, too, western allied casualties would have been much greater without the stubborn resistance of their Asian ally.Full article by Richard Overy, writing in The Guardian.
In the end, the western freedom to plan and execute a global strategy depended on the ability of the Soviet and Chinese forces to hold the main enemies at bay while western air forces bombed the Axis motherlands flat. When victory is celebrated tomorrow, it is important that we pause to remember the almost 50 million Soviets and Chinese who perished to contain the imperial aggression of Germany and Japan.