In the early 20th century, the Manchu state quickly declined and the revolutionary ideas developed. In 1911, the Republic of China replaced the state of Manchuria.
The intellectuals and statesmen of outer Mongolia proclaimed independence of the country. The new state of outer Mongolia was a theocracy, so the religous leader, called Bogd, was also the political leader. In 1913, a delegation of representatives of outer Mongolia, led by T. Namnansuren, visited the Russian Empire in order to find a support to secure independence. They wanted outer Mongolia to be internationally recognised, but they failed.
In 1915, in Kyakhta, discussions began between outer Mongolia and the Republic of China. Moscow and Beijing refuted to recognise the independence of outer Mongolia, and granted only an autonomous status.
In 1919, the Republican government of China abolished the autonomy and sent troops to outer Mongolia. The aim was to secure the Chinese interests in Mongolia, in the cas where Russians, muddled since 1917, wanted to extend there. The Mongolian independentist leaders resisted in many areas of the country.
In 1921, after revolutionary changes, Mongolia found its independence back and formed a theocratic state. This time, the government restricted the powers of the 8th Bogd. When the Bogd died in 1924, the revolutionary leaders transformed Mongolia in a republic and adoped the first constitution. The leaders of the state, helped by Soviet councillors, chose a communist direction for Mongolia.
The republican form brought several reforms. The society could not have classes, so the nobility gave up its titles and privileges. The occidental medicine, the technology and education appeared in Mongolia and marked the end of old practices.
The 1930's were crual. As in any communist state at that period, political purges seriously affected the society. The system was responsible of the death of thousands of innocent persons wrongly accused.
In 1939, Mongolia entered a major conflict against Japan along the eastern border of Mongolia (incident of Khakhingol). The fights between Japanese and Mongolian patrols that started in 1936 degenerated into in a majorborder confrontation. The Soviet army helped Mongolians, and together, they beat the Japanese forces and made the border secure.
In 1945, the Chinese government recognised independence of Mongolia. Mongolia became an ex officio member of the international community, and joined the United Nations in 1961.
Until the end of the 1980's, Mongolia was a communist state flawlessly aligned on the Soviet Union. But the world was changing, and also was the case for Mongolia. In December 1989, the democrat opposition asked political reforms and organised important protests. In 1992, Mongolia adopted a new constitution that guarantees an open democracy and economic changes.