The Soviet invasion of Manchuria 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. Soviet gains on the continent were Manchukuo, Mengjiang 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.