The Soviet Union declared war on Japan on August 8, 1945, before Japan's formal surrender.
Soviet Foreign Minister Vyacheslav Molotov informed Japan's ambassador in Moscow that the Soviet Union was entering the war. The declaration took effect at midnight on August 9, Moscow time, when Soviet forces began operations against Japanese forces in Manchuria and other areas of Japanese-controlled territory.
The Soviet move followed a commitment made at the Yalta Conference and came shortly after the United States atomic bombing of Hiroshima. The Soviet offensive rapidly defeated Japan's Kwantung Army and occupied large areas in northeastern Asia.
The date is often confused with August 9 because the invasion began after the declaration took effect across time zones. It is also distinct from August 15, when Hirohito's surrender announcement was broadcast, and September 2, when Japan signed the formal instrument.