The Second World War was an unparalleled calamity for the Soviet Union. As many as 27 million Soviet soldiers and civilians died as a result of the conflict that started with the German invasion of Poland in September 1939 and ended with the Japanese surrender in August 1945.
Consumed by this existential struggle along its western border, the Soviet Union was a comparatively minor factor in the Pacific War until the very end. Yet Moscow's timely intervention in the war against Japan allowed it to expand its influence along the Pacific Rim.
With the breakdown of Allied unity soon heralding the onset of the Cold War, Soviet gains in Asia also left a legacy of division and confrontation, some of which endure into the present.