ノモンハン事件
After the Japanese invasion of neighboring Manchuria in 1931, Mongolia was threatened on this front. During the Soviet-Japanese Border War of 1939, the Soviet Union successfully defended Mongolia against Japanese expansionism. Mongolia fought against Japan during the Battles of Khalkhin Gol in 1939 and during the Soviet–Japanese War in August 1945 to liberate Inner Mongolia from Japan and Mengjiang.