On what date did the Soviet Union declare war on Japan in World War II?

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

Foreign Minister Vyacheslav Molotov informed Japan’s ambassador in Moscow that the Soviet government considered itself at war with Japan from 9 August. The declaration fulfilled a commitment made to the other Allied powers at the Yalta Conference, where the Soviet Union had agreed to enter the war against Japan after Germany’s defeat.

The Soviet declaration came three months after Germany surrendered and while Japan was still fighting the United States, Britain, China, and other Allied nations. Soviet forces began their offensive shortly after midnight on 9 August, attacking Japanese positions in Manchuria, Korea, southern Sakhalin, and the Kuril Islands.

The date can cause confusion because the declaration was delivered on 8 August in Moscow, while the invasion began on 9 August in East Asia. The Soviet entry into the war, the atomic bombing of Hiroshima, and the bombing of Nagasaki all occurred during the final days before Japan’s surrender.