Soviet forces invaded Manchuria when they opened their 1945 offensive against Japan.
The Soviet invasion began on August 9, 1945, against Manchukuo, Japan's puppet state in northeastern China. The Red Army attacked from several directions with a large, mechanized force, overwhelming the Japanese Kwantung Army.
The campaign also spread into Inner Mongolia, northern Korea, southern Sakhalin, and the Kuril Islands. Manchuria, however, was the central theater and the region named in the campaign's usual title.
Japan had maintained a powerful military presence there, but the Kwantung Army was weaker than it had been earlier in the war because experienced units had been transferred to other fronts. Its defeat removed Japan's hope of using Soviet mediation and contributed to the crisis that produced surrender.