What did the Soviet Union do to Japan on 8 August 1945?

The Soviet Union declared war on Japan on 8 August 1945.

The declaration came late that day in Moscow, and Soviet forces began attacking Japanese positions shortly afterward, including in Manchuria. The action violated the Soviet-Japanese Neutrality Pact and fulfilled commitments the Soviet Union had made to the other Allied powers.

The timing was crucial. Hiroshima had been bombed by the United States on 6 August, and Nagasaki was bombed on 9 August. Japanese leaders therefore faced both the atomic bombings and the sudden opening of a major Soviet front in Asia.

The Soviet declaration is often left out of simplified accounts that attribute Japan’s surrender only to the atomic bombs. Historians continue to debate the relative weight of the bombings, Soviet entry, and Japan’s internal political crisis. The immediate historical fact is clear: Soviet entry sharply changed Japan’s strategic situation just days before Hirohito’s broadcast.