Manchukuo was the Japanese puppet state in Manchuria invaded by the Soviet Union in August 1945.
Japan established Manchukuo in 1932 after occupying Manchuria. Although presented as an independent empire, it was dominated by Japan and relied heavily on Japanese military and political control. Former Qing emperor Puyi served as its head of state and later emperor under the Japanese-backed regime.
The Soviet invasion began on 9 August 1945. Red Army forces crossed into Manchukuo in a large, coordinated offensive that rapidly broke through Japanese defenses. The campaign also reached Inner Mongolia, northern Korea, southern Sakhalin, and the Kuril Islands.
Manchukuo collapsed during the offensive. Puyi abdicated after the Soviet advance, and the territory was later returned to Chinese administration after the war. The invasion is important to the surrender story because Japanese leaders had expected Soviet neutrality or mediation, not a major attack on their continental empire.