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When did Outer Mongolia become independent?

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Wide autumn valley with golden grass in the foreground and low, tree-covered mountains of the Greater Khingan Range in the distance under a clear sky. — Inner Mongolia Da Hinggan (Greater Khingan) Range, southeast of Hailar, Inner Mongolia Autonomous Region, China.

Following the 1911 Chinese Revolution, Outer Mongolia declared its independence from the Qing dynasty. However, this status was initially unsettled; while the Bogd Khan declared independence, the region only achieved autonomy under Chinese suzerainty through subsequent treaties in 1913 and 1915.123

Following a period of occupation and conflict, nationalist revolutionaries—with the assistance of the Soviet Union—captured the capital in July 1921. The Mongolian People’s Republic was subsequently proclaimed in November 1924, solidifying its independence as a sovereign state, though it remained a client state of the Soviet Union until the early 1990s.132