The Soviet invasion of Manchuria rapidly defeated Japan's Kwantung Army in August 1945.
The Kwantung Army had been Japan's major military force in Manchuria and was associated with the defense and administration of Manchukuo, Japan's puppet state. By 1945, however, many experienced units had been transferred from Manchuria to other fronts, leaving the formation less powerful than its earlier reputation suggested.
The Soviet offensive began on August 9 from several directions. Soviet forces used large mechanized formations, armor, aircraft, and coordinated operations across difficult terrain. The rapid advance overwhelmed Japanese defenses and cut communications between units. The campaign also affected Japanese positions in Inner Mongolia, northern Korea, southern Sakhalin, and the Kuril Islands.
The Kwantung Army's defeat contributed to the crisis that led Japan to accept surrender terms. Its formal surrender order was not immediately obeyed everywhere, so isolated fighting continued after Hirohito's August 15 announcement. The final surrender document was signed on September 2.