Populated by a mixture of ethnic Laos, Thais and various hill tribes, the Lan Xang empire lasted for three centuries while fighting off successive invasions from Vietnam, Siam (Thailand) and Burma. Internal power struggles in the 18th century were exploited by its neighbours, notably Siam which finally conquered Vientiane in 1779. The city was later destroyed by the Siamese and the remains of Lan Xang absorbed into Siam. The 19th century was a period of political turmoil in which rival powers with shifting alliances fought for control of the territory. The Siamese were the dominant power until the arrival of the French, who had already established a firm grip in neighbouring Vietnam, in the 1870s. Laos then became part of French Indo-China, which lasted until the 1950s, with the exception of a brief period of Japanese occupation during World War II.