Negotiations continued for eight months as the Mongolian representatives firmly defended the independence of the country, but finally the government of Mongolia had to accept Russia's position. However, Outer Mongolia remained effectively outside the control of the Chinese, who on the other hand controlled Barga, Dzungaria, Tuva, Upper Mongolia, and Inner Mongolia in 1915. On 2 February 1913, Mongolia and Tibet signed a treaty of friendship and alliance. Mongolian agents and Bogd Khaan (he was a Tibetan) disrupted Soviet secret operations in Tibet to change its regime in the 1920s. Following the Russian Revolution of October 1917, China revived its claims to Outer Mongolia, aiming at its conversion into a common Chinese province. In late 1919, the Chinese general Xu Shuzheng occupied Urga after suspicious deaths of Mongolian patriotic nobles 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 and Damdinsüren (died in the prison under brutal torture) were arrested and imprisoned. The Chinese had tightened their control of Mongolia by this time. Russian White Guard troops led by Baron Ungern von Sternberg, who had been defeated in the Civil War in Transbaikalian Siberia, invaded Mongolia in October 1920. Baron Ungern sought allies to defeat the Soviet Union. 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, Ungern's force (mainly Mongolian volunteer cavalrymen, Buryat and Tatar cossacks of Russia) drove the Chinese forces out of the Mongolian capital. One part of the Chinese forces fled to the south to China, and another to the north of Mongolia to enter negotiations with the Far Eastern Republic (a puppet state created by Soviet Russia). The Bogd Khaan's monarchic power and his government were restored. Bogd Khan failed in his efforts to get aid from Japan and the United States for regaining the independence of Mongolia from China. Later the Chinese forces were defeated by Baron Ungern, but at the same time the Mongolian People's Party (MPP) had been established.