The Manchurian Strategic Offensive Operation began on 9 August 1945, with the Soviet invasion of the Japanese puppet state of Manchukuo and was the last campaign of the Second World War and the largest of the 1945 Soviet–Japanese War which resumed hostilities between the Soviet Union and the Empire of Japan after almost six years of peace. Soviet gains on the continent were Manchukuo, Mengjiang (Inner Mongolia) and northern Korea. The rapid defeat of Japan's Kwantung Army has been argued to be a significant factor in the Japanese surrender and the end of World War II, as Japan realized the Soviets were willing and able to take the cost of invasion of its Home Islands, after their rapid conquest of Manchuria and Invasion of South Sakhalin island.