The Mongolian Revolution of 1921 began on 18 March, when 400 volunteer troops led by Sukhbaatar attacked the 2,000-man Chinese garrison in Kyakhta at the northern frontier of Mongolia. The Mongolian volunteer troops and units of the Soviet Red Army advanced to the south, annihilating the remainder of the defeated Chinese troops and Ungern's White troops. The main battles undertaken by the Mongolian troops took place at Tujiin Nars against the Chinese and at Zelter and Bulnai against the White troops. Simultaneously, Khatanbaatar Magsarjav, who had been sent by Baron Ungern to the western provinces, revolted and allied himself with the MPP. He defeated the White troops led by Kazantsev, Vandanov, and Bakich. Mongolian and Soviet troops led by Khasbaatar and Baikalov withstood a long encirclement by the Whites at Lake Tolbo (in present-day Bayan-Ölgii aimag). Baron Ungern, after a conspiracy, was deserted by his troops and captured by a detachment of the Red Army. The MPP troops and Russian Red Army troops entered Urga in July 1921.
