The Laotians are descendants of Thai tribes that were pushed southward from Yunnan, China, in the 13th cent. and gradually infiltrated the territory of the Khmer Empire. In the mid-14th cent. a powerful kingdom called Lan Xang was founded in Laos by Fa Ngoun (1353–73), who is also credited with the introduction of Theravada Buddhism and much of Khmer civilization into Laos. Lan Xang waged intermittent wars with the Khmer, Burmese, Vietnamese, and Thai, and by the 17th cent. it held sway over sections of Yunnan, China, of S Myanmar, of the Vietnamese and Cambodian plateaus, and large stretches of N Thailand. In 1707, however, internal dissensions brought about a split of Lan Xang into two kingdoms: Luang Phabang in upper (northern) Laos and Vientiane in lower (southern) Laos. During the next century the two states, constantly quarreling, were overrun by the armies of neighboring countries.