<Dd> French--Thai </Dd> <Dd> Ecuadorian--Peruvian War </Dd> <P> The Soviet--Japanese War (Russian: Советско - японская война; Japanese: ソ連 対日 参戦, "Soviet Union entry into war against Japan") was a military conflict within the Second World War beginning soon after midnight on August 9, 1945, with the Soviet invasion of the Japanese puppet state of Manchukuo . The Soviets and Mongolians terminated Japanese control of Manchukuo, Mengjiang (Inner Mongolia), northern Korea, Karafuto, and the Chishima Islands . The defeat of Japan's Kwantung Army helped in the Japanese surrender and the termination of World War II . The Soviet entry into the war was a significant factor in the Japanese government's decision to surrender unconditionally, as it made apparent the Soviet Union would no longer be willing to act as a third party in negotiating an end to hostilities on conditional terms . </P> <P> At the Tehran Conference in November 1943, Stalin agreed that the Soviet Union would enter the war against Japan once Nazi Germany was defeated . At the Yalta Conference in February 1945, Stalin agreed to Allied pleas to enter World War II's Pacific Theater within three months of the end of the war in Europe . On July 26, the US, UK and China made the Potsdam Declaration, an ultimatum calling for the Japanese surrender which if ignored would lead to their "prompt and utter destruction". </P>

When did the soviets declared war on japan