Yunnan Province has its capital at Kunming and borders Myanmar, Laos, and Vietnam. 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. Yunnan is rich in natural resources and has the largest diversity of plant life in China. It became the seat of a Tibeto-Burman speaking kingdom known as the Kingdom of Nanzhao in the 8th century AD. The "Burma Road" was a highway extending about 1,100 kilometres (680 mi) through mountainous terrain from Lashio, northeast Burma northeastward to Kunming, China. Undertaken by the Chinese after the start of the Sino-Japanese War in 1937 and completed in 1938, it was a vital transportation route for wartime supplies to the Chinese government from Rangoon and shipped by railroad to Lashio from 1938 to 1946.