The Soviet Union declared war on Japan on 8 August 1945, shortly before Japan’s surrender. Foreign Minister Vyacheslav Molotov informed Japanese ambassador Naotake Satō in Moscow that the Soviet government would consider itself at war with Japan from 9 August.
The declaration followed a secret Allied agreement made at the Yalta Conference. The Soviet Union had promised to enter the war against Japan after Germany’s defeat, and it ended its neutrality toward Japan in August 1945.
At one minute past midnight on 9 August, Soviet forces began a large-scale invasion of Japanese-held Manchuria. They attacked from several directions, overwhelming the Kwantung Army and also advancing into northern Korea, southern Sakhalin, and the Kuril Islands.
This event is sometimes confused with the invasion’s start date: the declaration was made on 8 August in Moscow, while the military offensive began on 9 August in the Far East. Soviet entry added major pressure on Japan alongside the atomic bombings and helped bring about its surrender.