The Soviet–Japanese War was a campaign of the Second World War that began with the Soviet invasion of Manchuria following the Soviet declaration of war against Japan on 8 August 1945. The Soviet Union and Mongolian People's Republic toppled the Japanese puppet states of Manchukuo in Manchuria and Mengjiang in Inner Mongolia, as well as northern Korea, Karafuto on the island of Sakhalin, and the Kuril Islands. The defeat of Japan's Kwantung Army helped bring about the Japanese surrender and the end of World War II. The Soviet entry into the war showed that the Soviet Union would not act as a third party in negotiating a conditional end to hostilities, and thus was a factor in the Japanese government's decision to surrender unconditionally.