The Soviet invasion of Japanese-occupied Manchuria began on August 9, 1945.
The offensive began shortly after midnight in the Soviet Far East, following the Soviet declaration of war on Japan late on August 8. Soviet and Mongolian forces attacked Japanese positions across Manchuria, Inner Mongolia, and northern Korea. The campaign is also known as the Manchurian Strategic Offensive Operation and, in some Western accounts, Operation August Storm.
The attack caught Japanese forces by surprise. The Kwantung Army had once been one of Japan's most powerful formations, but many experienced troops and equipment had been transferred to other fronts. Soviet forces advanced rapidly, taking major positions and defeating Japanese resistance in much of the region.
The invasion began between the atomic bombings of Hiroshima and Nagasaki and was an important factor in Japan's decision to surrender. The Kwantung Army's formal surrender followed on August 16, but fighting in some areas continued until the September 2 signing.