The Soviet Union declared war on Japan on August 8, 1945, and began military operations the next day.
The Soviet declaration fulfilled a commitment made at the Yalta Conference. The Soviet government had agreed to enter the war against Japan after Germany’s defeat, although Japan and the Soviet Union had maintained a neutrality pact during much of the Pacific War.
Soviet forces invaded Japanese-held territories in Manchuria, Korea, Sakhalin, and the Kuril Islands. The campaign, often called the Soviet–Japanese War, rapidly defeated the Japanese Kwantung Army in Manchuria. The Soviet entry destroyed Japanese hopes that Moscow might mediate a better peace settlement with the Western Allies.
The timing remains central to historical discussions of Japan’s surrender. The Soviet declaration came between the Hiroshima bombing on August 6 and the Nagasaki bombing on August 9. Historians continue to debate the relative importance of the atomic bombings, Soviet entry, and Japan’s internal political crisis.