Study this picture: Atomic weapons were scary, but so was the full-on might of the Red Army.
Key point: Historians will debate exactly what caused Tokyo to surrender. However, some of the credit must go to the surprise Soviet invasion of Japanese-occupied Manchuria.
To the Soviet military, it is known as the Manchurian Strategic Offensive Operation. Although it had no official name to the Japanese, it has become known in the West as Operation August Storm. It was the greatest defeat in Japanese military history, yet few outside the circles of Japanese and Soviet history are even aware that it occurred. It ensured the end of World War II as much as the dropping of the atomic bombs on Hiroshima and Nagasaki did, yet it is often ignored in Western studies of the war.