The Soviet invasion of Manchuria, formally known as the Manchurian strategic offensive operation () or simply the Manchurian operation (), began on 9 August 1945 with the Soviet invasion of the Japanese puppet state of Manchukuo. It was the largest campaign of the 1945 Soviet–Japanese War, which resumed hostilities between the Union of Soviet Socialist Republics and the Empire of Japan after almost six years of peace. Since 1983, the operation has sometimes been called Operation August Storm after U.S. Army historian David Glantz used this title for a paper on the subject. Soviet gains on the continent were Manchukuo, Mengjiang (the northeast section of present-day Inner Mongolia) and northern Korea. The Soviet entry into the war and the defeat of the Kwantung Army was a significant factor in the Japanese government's decision to surrender unconditionally, as it became apparent that the Soviet Union had no intention of acting as a third party in negotiating an end to hostilities on conditional terms. Summary As agreed with the United Kingdom and the United States (Western Allies) at the Tehran Conference in November 1943 and the Yalta Conference in February 1945, the Soviet Union entered World War II's Pacific Theater within three months of the end of the war in Europe. The invasion began on 9 August 1945, exactly three months after the German surrender on May 8 (9 May, 0:43 Moscow time). Although the commencement of the invasion fell between the American atomic bombing of Hiroshima, on 6 August, and only hours before the Nagasaki bombing on 9 August, the timing of the invasion had been planned well in advance and was determined by the timing of the agreements at Tehran and Yalta, the long-term buildup of Soviet forces in the Far East since Tehran, and the date of the German surrender some three months earlier; on August 3, Marshal Vasilevsky reported to Premier Joseph Stalin that, if necessary, he could attack on the morning of 5 August. At 11 p.m. Trans-Baikal (UTC+10) time on 8 August 1945, Soviet foreign minister Vyacheslav Molotov informed Japanese ambassador Naotake Satō that the Soviet Union had declared war on Japan, and that from 9 August the Soviet government would consider itself to be at war with Japan. At one minute past midnight Trans-Baikal time on 9 August 1945, the Soviets commenced their invasion simultaneously on three fronts to the east, west and north of