Japan’s main army force in Manchuria defeated by the Soviet offensive in August 1945 was the Kwantung Army.
The Kwantung Army was the Imperial Japanese Army formation responsible for much of Japan’s military presence in Manchuria. It had once been regarded as an elite force and played a central role in the creation and defense of the Japanese puppet state of Manchukuo.
By 1945, however, many experienced units and weapons had been transferred to other fronts. The Soviet invasion began on August 9 with a massive, coordinated attack using armor, artillery, aircraft, and mechanized forces. The Kwantung Army was rapidly outmatched, and its defeat removed Japan’s hope that the Soviet Union might help negotiate a favorable settlement.
The force formally surrendered on August 16, although fighting and disarmament continued until the broader Japanese surrender was completed. The Kwantung Army should not be confused with Japan’s China Expeditionary Army, which operated mainly in occupied central and eastern China.