The Kwantung Army was Japan’s major army formation in Manchuria when the Soviet invasion began in August 1945.
The Soviet Union invaded Japanese-occupied Manchuria on August 9, 1945, attacking the Japanese puppet state of Manchukuo and related positions in Inner Mongolia and Korea. The Kwantung Army, once regarded as an elite Japanese force, was badly weakened by transfers of experienced troops to other fronts.
Soviet forces advanced rapidly using a large-scale offensive across difficult terrain. The defeat of the Kwantung Army removed Japan’s hope that the Soviet Union might mediate a conditional peace with the Western Allies.
The invasion was one of several major pressures leading to Japan’s surrender. Historians debate the relative importance of the Soviet attack and the atomic bombings, but the Kwantung Army’s collapse clearly changed Japan’s strategic situation. Fighting in some areas continued after the August 15 announcement.