The Kwantung Army’s defeat in Manchuria helped bring about Japan’s surrender in August 1945.
The Kwantung Army was Japan’s major military force in Manchuria, where it had supported the Japanese-controlled state of Manchukuo. The Soviet Union declared war on Japan on August 8, 1945, and invaded Japanese-held Manchuria shortly after midnight on August 9.
The Soviet offensive attacked from several directions and rapidly overwhelmed Japanese forces. Its entry destroyed Japanese hopes that Moscow might mediate a negotiated peace with the Allies and demonstrated that Japan faced a major new enemy on the Asian mainland.
Japan’s surrender resulted from several pressures, including the atomic bombings of Hiroshima and Nagasaki, the Soviet invasion, blockade, and conventional military defeat. Historians continue to debate the relative weight of those factors, but the Kwantung Army’s collapse was an important military and strategic shock.