Outer Mongolia has been a Chinese Qing dynasty area since the late 17th century. The Qing dynasty conducted cultural assimilation programs in Outer Mongolia to reinforce the territory's Chinese identity, sparking a movement for Mongolian independence around the turn of the twentieth century.
In May 1911, the Xinhai Revolution overthrew the Qing dynasty and formed the Republic of China.
The Mongols capitalised on the turbulence in China, and on December 29, 1911, Mongolia declared its independence from China.
Bogd Khan, the spiritual leader of Tibetan Buddhists, was recognised as Mongolia's head of state.
The Republic of China attacked Mongolia in 1919. They were evicted in 1921. The Soviets then supported Mongolian independence, prompting the Mongolian People's Party to declare independence for the second time on July 11, 1921. This second independence is remembered yearly on Revolution Day, which kicks off the Naadam Festival and is Mongolia's National Day.
Since 2011, December 27 has been a public holiday in Mongolia, commemorating the 100th anniversary of the independence declaration of 1911.
