Kingdom of Vientiane
Historically, the main suzerain or overlord states were the Khmer Empire of Cambodia; Srivijaya of South Sumatra; the successive kingdoms of Medang, Kediri, Singhasari and Majapahit of Java; the Ayutthaya Kingdom of Thailand; Champa and early Đại Việt. China occupies a special place in that the others often in turn paid tribute to China, although in practice the obligations imposed on the lesser kingdoms were minimal. The most notable tributary states were post-Angkor Cambodia, Lan Xang (succeeded by the Kingdom of Vientiane and Luang Prabang) and Lanna. Cambodia in the 18th century was described by the Vietnamese emperor Gia Long as "an independent country that is slave of two" (Chandler p. 119). The system was eventually ended by the arrival of the Europeans in the mid-19th century. Culturally, they introduced Western geographical practices, which assumed that every area was subject to one sovereign. Practically, the colonisation of French Indochina, Dutch East Indies, British Malaya and Burma brought pressure from the colonisers for fixed boundaries to their possessions. The tributary states were then divided between the colonies and Siam, which exercised much more centralised power but over a smaller area than thitherto.