The Soviet Union declared war on Japan on 8 August 1945, joining the final offensive against Japan.
Soviet Foreign Minister Vyacheslav Molotov informed Japan’s ambassador in Moscow that the Soviet government was at war with Japan. Soviet forces began invading Japanese-held Manchuria shortly after midnight on 9 August, attacking on several fronts against the Kwantung Army.
The move followed a secret Allied understanding that the Soviet Union would enter the Pacific war after Germany’s defeat. Before August 1945, the Soviet Union and Japan had maintained the Soviet–Japanese Neutrality Pact, although Moscow later repudiated it.
The declaration occurred between the atomic bombings of Hiroshima and Nagasaki and added a major military and diplomatic shock for Japan. It is distinct from the United States’ declaration of war against Japan in December 1941. Japan announced acceptance of the Potsdam terms on 15 August, and the formal surrender followed on 2 September.