The Soviet invasion of Japanese-held Manchuria began on 9 August 1945.
The offensive, formally known as the Manchurian Strategic Offensive Operation, began shortly after the Soviet Union declared war on Japan. Soviet forces attacked Japanese-held Manchuria and the Japanese puppet state of Manchukuo from multiple directions just after midnight Trans-Baikal time.
The Japanese Kwantung Army had once been regarded as a powerful force, but it was weakened by transfers of troops and equipment to other fronts. The Soviet offensive rapidly seized territory in Manchuria and also affected Japanese positions in Inner Mongolia, southern Sakhalin, and the northern Korean Peninsula.
The invasion coincided with the final crisis of the Japanese government. Japan had already suffered the atomic bombing of Hiroshima on 6 August, and Nagasaki was bombed on 9 August. The Soviet attack and the atomic bombings are both treated as major factors in Japan’s decision to surrender.