Soviet forces invaded Manchuria on August 9, 1945, as Japan’s defeat accelerated.
The Soviet Union declared war on Japan late on August 8 and began its invasion shortly after midnight on August 9. The campaign targeted Manchuria, then controlled by Japan’s puppet state of Manchukuo, and involved simultaneous Soviet offensives from the east, west, and north.
Japan had hoped the Soviet Union might mediate between Tokyo and the Western Allies, but the Soviet attack ended that possibility. The invasion rapidly overwhelmed the Japanese Kwantung Army, which had once been one of Japan’s strongest forces. The Soviet offensive, together with the atomic bombings of Hiroshima and Nagasaki, is widely regarded as a major factor in Japan’s decision to surrender.