In the early 20th century, the Manchurian state declined rapidly and revolutionary ideas of the era took hold.

In 1911, the Republic of China replaced the Manchurian state. Intellectual leaders and statesmen of Outer Mongolia also brought about change and proclaimed the country's independence. The new state of Outer Mongolia was a theocracy. This meant that the Bogd, who was the religious leader, held secular political power.

In 1913, a delegation of representatives from Outer Mongolia led by T. Namnansüren visited the Russian Empire to seek support for securing independence. They failed in their mission to gain international recognition for Outer Mongolia.

In 1915, discussions between Outer Mongolia and the Republic of China began in the city of Kyakhta. Moscow and Peking refused to recognize the independence of Outer Mongolia and granted Mongolia only autonomous status.

In 1919, the Republican government of China abolished autonomy and sent troops into Outer Mongolia. The purpose of this high-risk operation was to secure Chinese interests in Mongolia in case the revolutionary Russians of 1917 sought to expand eastward. Mongolian independence leaders resisted in several regions of the country.

In 1921, following revolutionary changes, Mongolia regained its independence and formed a theocratic state. This time, the powers of the 8th Bogd were restricted by the government.

When the Bogd died in 1924, revolutionary leaders transformed Mongolia into a republic and adopted its first constitution. The leaders of the state, aided by Soviet advisors, chose a communist direction for Mongolia. The republican form of government brought numerous reforms to society. Society was to be classless, so the nobility abandoned all titles and privileges. Western medicine, technology, and education entered Mongolia, ending old practices.

The 1930s were brutal. As in all communist states of that era, political purges seriously affected society. The regime was responsible for the deaths of thousands of innocent people wrongly accused.

In 1939, Mongolia engaged in a major conflict with the Japanese along Mongolia's eastern border, known as the Khalkhin Gol Incident. Minor skirmishes between Japanese and Mongolian patrols since 1936 escalated into a major border confrontation. The Soviet Army came to the aid of the Mongols. The Soviet/Mongolian army defeated the Japanese forces and secured the eastern border.

In 1945, the Chinese government recognized Mongolia's independence. Mongolia became a full member of the international community and joined the United Nations in 1961. Mongolia remained a communist state impeccably aligned with the Soviet Union until the late 1980s. The world was changing, and so was Mongolia.

In December 1989, the democratic opposition called for political reforms and organized major demonstrations.

Finally, in 1992, Mongolia adopted a new Constitution guaranteeing an open democracy and economic reforms.