Following the Russian Revolution of October 1917, China regained its claims to Outer Mongolia aiming at its conversion into a common Chinese province. In late 1919, the Chinese general Xu Shuzheng occupied Urga and forced the Bogd Khaan and the leading nobles to sign a document renouncing Mongolia’s independence. Leaders of Mongolia’s national independence movement, such as Magsarjav or Damdinsuren (died in the prison under brutal torture) were arrested and imprisoned. The Chinese had tighted their control of Mongolia by this time.

Russian White Guard troops led by Baron R.F. von Ungern-Sternberg (Baron Ungern von Sternberg), who had been defeated in the Civil War in Transbaikalian Siberia, invaded Mongolia in October 1920. In October–November 1920, Ungern’s troops assaulted the capital, Niislel Khuree, known to Europeans under the name Urga (now Ulaanbaatar), several times but were repelled with heavy losses. Ungern entered contacts with Mongolian nobles and lamas and received Bogd Khaan’s edict to regain independence. On 2–5 February 1921, after fighting a huge battle, he drove the Chinese forces out of Mongolian capital.

Source: Wikipedia, published under the GNU FDL. Retrieved 2013-08-14