Laos is geographically isolated and mountainous, bounded by the Annamite Range in the east, forming a traditional political and cultural boundary with Vietnam (a more Chinese influenced Sinitic culture). Much of the western borders of Laos are formed by the Mekong River which provided the major means of inland trade despite limited navigability along the river's length. Prior to the 20th century Lao principalities and the Kingdom of Lan Xang extended to the Sipsong Panna (China), Sipsong Chau Tai (Vietnam), and Khorat Plateau (today the northeast of Thailand) where the river was used as a transportation artery to connect Lao peoples on both the right and left banks. However, the political history of Laos has been complicated by frequent warfare and colonial conquests by European and regional rivals. As a result, Laos today has cultural influence from France, Thailand, China, Vietnam, Burma and Cambodia. The history of Laos is unique with a national character defined by its diversity in both culture and customs.