Mongolia /mɒŋˈɡoʊliə/ is a landlocked country in east-central Asia. It is bordered by Russia to the north and China to the south, east and west. Ulaanbaatar, the capital and also the largest city, is home to about 45% of the population. Mongolia's political system is a parliamentary republic.The area of what is now Mongolia has been ruled by various nomadic empires, including the Xiongnu, the Xianbei, the Rouran, the Gökturks, and others. In 1206, Genghis Khan founded the Mongol Empire, and his grandson Kublai Khan conquered China to establish the Yuan Dynasty. After the collapse of the Yuan, the Mongols retreated to Mongolia and resumed their earlier pattern of factional conflict and occasional raids on the Chinese borderlands. In the 16th and 17th centuries, Mongolia came under the influence of Tibetan Buddhism.At the end of the 17th century, all of Mongolia had been incorporated into the area ruled by the Manchu's Qing Dynasty. During the collapse of the Qing Dynasty the Mongols established Temporary Government of Khalkha in 30 November 1911. On 29 December 1911 Mongolia declared independence from the Qing Dynasty and this National Liberation Revolution ended the Manchu's rule that lasted 220 years.The country came under Soviet influence, resulting in the proclamation of the Mongolian People's Republic as a Soviet satellite state in 1924. After the breakdown of communist regimes in Europe in late 1989, Mongolia saw its own democratic revolution in early 1990; it led to a multi-party system, a new constitution of 1992, and transition to a market economy.At 1,564,116 square kilometres, Mongolia is the 19th largest and the most sparsely populated independent country in the world, with a population of around 2.9 million people. It is also the world's second-largest landlocked country after Kazakhstan. The country contains very little arable land, as much of its area is covered by steppe, with mountains to the north and west and the Gobi Desert to the south.Approximately 30% of the population are nomadic or semi-nomadic. The predominant religion in Mongolia is Tibetan Buddhism, and the majority of the state's citizens are of Mongol ethnicity, although Kazakhs, Tuvans, and other minorities also live in the country, especially in the west. About 20% of the population live on less than US$1.25 per day. Mongolia joined the World Trade Organization in 1997 and seeks to expand its participation in regional economic and trade regimes. According to a 2011 World Health Organization survey, Mongolia has some of the worst air pollution in the world, with an annual average of 279 micrograms of "PM10" particles per cubic metre.