From the end of the 17th century, Outer Mongolia had been a territory of the Chinese Qing dynasty. A move for Mongolian independence had been stoked at the start of the 20th century after the Qing dynasty implemented cultural assimilation policies in Outer Mongolia to strengthen the Chinese identity of the territory. 

In May 1911, the Xinhai Revolution led to the overthrow of the Qing dynasty and established the Republic of China. 

The turmoil in China was pounced upon by the Mongols, and on December 29th 1911, Mongolia officially declared its independence from China. 

The spiritual leader of the Tibetan Buddhists was proclaimed Bogd Khan of Mongolia, becoming the head of state. 

The Republic of China invaded Mongolia in 1919. They were ousted in 1921. The Soviets then supported Mongolian independence leading to the Mongolian People’s Party declaring independence for a second time on July 11th 1921. This second independence is commemorated each year on Revolution Day which marks the start of the Naadam Festival and is the National Day of Mongolia. 

December 27th has been a public holiday in Mongolia since 2011, the 100th anniversary of the 1911 independence declaration. 

With only three million people in its 604,000 square miles, Mongolia is the world’s most sparsely populated sovereign state.