October 20, 1945 (September 15) Yiyou, Outer Mongolia declared independence. signed

1924 Russian Chinese Outline Agreement provides that the Russian Government recognize Outer Mongolia as part of China's territory. February 1945 Yalta Conference, Summit of the Soviet Union, the United States, Britain, provides: Outer Mongolia (Mongolian People's Republic), the status quo to be maintained. On August 14 of the same year, the Chinese Nationalist government as stipulated in the annex of the Sino-Soviet Treaty signed with the Soviet Union: the Soviet Union will respect the political independence and territorial integrity of Outer Mongolia. The Chinese Nationalist government statement, after the defeat of Japan, such as Outer Mongolia citizen voting confirmed this desire, when the Chinese government to recognize Outer Mongolia's independence. October 20, 1945, Outer Mongolia held a referendum to declare independence.