Yunnan is a province of the People's Republic of China, located in the far southwest of the country. It spans approximately 394,000 square kilometres (152,000 sq mi) and has a population of 45.7 million in 2009. The capital of the province is Kunming, formerly also known as Yunnan. The province borders Vietnam, Laos, and Burma.Yunnan is situated in a mountainous area, with high elevations in the northwest and low elevations in the southeast. Most of the population lives in the eastern part of the province. In the west, the altitude can vary from the mountain peaks to river valleys as much as 3,000 metres (9,800 ft). Yunnan is rich in natural resources and has the largest diversity of plant life in China. Of the approximately 30,000 species of higher plants in China, Yunnan has perhaps 17,000 or more.[4] Yunnan's reserves of aluminium, lead, zinc and tin are the largest in China, and there are also major reserves of copper and nickel.The Han Empire first recorded diplomatic relations with the province at the end of the 2nd century BC. It became the seat of a Sino-Tibetan-speaking kingdom of Nanzhao in the 8th century AD. Nanzhao was multi-ethnic, but the elite most-likely spoke a northern dialect of Yi. The Mongols conquered the region in the 13th century, with local control exercised by warlords until the 1930s. From the Yuan dynasty onward, the area was part of a central-government sponsored population movement towards the Southwestern frontier, with 2 major waves of migrants arriving from Han-majority areas in northern and southeast China.[5] As with other parts of China's southwest, Japanese occupation in the north during World War II forced another migration of majority Han people into the region. These two waves of migration contributed to Yunnan being one of the most ethnically diverse provinces of China, with ethnic minorities accounting for about 34 percent of its total population. Major ethnic groups include Yi, Bai, Hani, Zhuang, Dai and Miao.