Official Languages: Lao
Established: 1713 AD/CE
Disestablished: 1904 AD/CE
The kingdom was sited on the eastern or Left Bank of the Mekong, south of the Right Bank principality of Khong Chiam where the Mun River joins; and east of where the Mekong makes a sharp bend to the west to return abruptly and flow southeasterly down to what is now Cambodia. Bassac, the capital city, was on the right bank, near where the Bassac River joins the Mekong, connecting to Phnom Penh.
Due to scarcity of information from the periods known as the Post-Angkor Period, the Khorat Plateau seems to have been largely depopulated, and Left Bank principalities began to repopulate the Right. In 1718, a Lao emigration in the company of an official in the service of King Nokasad founded Muang Suwannaphum as the first recorded population of Lao in the Chi River valley—indeed anywhere in the interior of the plateau.
At the beginning the 19th century, and ignoring the worldwide agricultural disaster accompanying the 1816 Year Without a Summer, Bassac was said to be on a prosperous trade route as the outlet for cardamon, rubber, wax, resin, skins, horns, and slaves from the east bank to Ubon, Khorat, and Bangkok. The region then fell victim to Siamese and French struggles to extend suzerainty.
After the Laotian Rebellion of 1826–1829, Suwannaphum lost its status and Champasak was reduced to vassalage. The Siamese-Cambodian War of 1831–1834 reduced the entire region to vassalage of the Nguyen Dynasty, a situation soon further complicated by the French striving in the same region to establish what was to become French Indochina.
Following the Franco-Siamese War of 1893, the Left Bank fell under French rule as an administrative block, with its royalty stripped of many privileges; French colonial administration of Lao kingdoms impoverished the region. The 1893 treaty called for a twenty-five-kilometer-wide demilitarized zone along the Right Bank, which made Siamese control impossible. It soon became a haven for lawless characters from both banks of the river. Lack of clear chains of authority resulted in turmoil in the whole region, and in what was known to the Siamese side as the "Holy Man's Rebellion". The Phra Phuttha Butsayarat or Phra Luk Buddha, palladium of the Kingdom of Champasak, Laos. The Phra Butsayarat was brought to the Kingdom of Lan Xang by King Setthathirath from the Kingdom of Lan Na in the 16th century, with several other significant statutes. In the 19th century the image was taken by the Kingdom of Siam to Bangkok. It currently resides in the Phra Buddha Rattanasathan (พระพุทธรัตนสถาน) ordination hall at the Grand Palace in Bangkok. Ong Keo and Ong Kommandam of the Bolaven Plateau Alak people, led the initial resistance against French control, which evolved into the Holy Man's Rebellion. The concomitant right-bank Holy Man's Rebellion of 1901–1902 was a short-lived phenomenon. Following legal action against captured local leaders of the movement, the Thai government considered the case of the rebellion closed. The right-bank dependencies were absorbed into the Siamese Northeast Monthon, Isan (มณฑลอีสาน), and the House of Na Champassak continued to rule autonomously. In 1904, prior to the Franco-Siamese Treaty, the kingdom's capital was transferred to the French rule and was placed under the control of French Cambodia. Despite historical claims by Cambodia, Champassak lost jurisdiction over the province of Stung Treng and in return regained the city of Champasak. In addition, the provinces of Kontum and Pleiku were ceded to French administration in Annam.