Yunnan was a province of the Han Dynasty (206 BC-220 CE) before it became the seat of a Tibeto-Burman speaking kingdom known as Nanzhao in the 8th century. 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. As with other parts of China's southwest; Japanese occupation in the north during World War II forced a migration of Chinese into the region. Ethnic minorities in Yunnan today account for about 34 percent of its total population. Major ethnic groups include Yi; Bai; Hani; Zhuang; Dai and Miao.