Which Soviet military operation began against Japan in August 1945 as surrender negotiations unfolded?

The Soviet invasion of Manchuria began against Japan as surrender negotiations unfolded in August 1945.

The Soviet Union declared war on Japan on 8 August 1945, and its forces launched a major offensive in Manchuria shortly after midnight on 9 August. The campaign targeted the Japanese-held territory of Manchukuo and the Kwantung Army, which had been one of Japan’s largest military formations.

The offensive rapidly overran Japanese positions across Manchuria, Inner Mongolia, southern Sakhalin, and the Kuril Islands. Its timing was strategically important. Japan had hoped that the Soviet Union might help mediate between Tokyo and the Western Allies, but the Soviet declaration destroyed that possibility and opened a new front against Japan.

The Soviet attack coincided with the bombing of Nagasaki on 9 August. Japanese leaders confronted the combined impact of the atomic bombings, Soviet entry into the war, and the growing likelihood of invasion. Emperor Hirohito supported acceptance of the Potsdam Declaration, which was announced to the public on 15 August.

Fighting continued in some areas after the announcement, and Soviet operations continued until Japanese forces surrendered locally.