The Lao Isan live in one of the most archaeologically rich areas of Southeast Asia. Farming has been carried out in the region for approximately 5,000 years. Some of the earliest evidence of the use of bronze anywhere in the world has been found in Udon Thani Province in the northern part of the Khorat Plateau. The Lao made their presence known in the region in the fourteenth century A.D. with the founding of the kingdom of Lan Chang, which straddled both sides of the Mekong and extended its power north to Yunnan and west to the northern Thai kingdom of Chiengmai. This kingdom dissolved in the early eighteenth century into a number of competing kingdoms including Luang Prabang, Champasak, and Vientiane. The latter two kingdoms controlled parts of what is now northeast Thailand. Champasak had tributaries on the Mun and Chi rivers in what is today a part of Ubon Ratchathani and Roi Et provinces. Vientiane, meanwhile, is thought to have controlled territories in present-day Loei, Nong Khai, and Nakhon Phanom provinces. The Siamese of Ayutthaya had taken control of Nakhon Ratchasima in the seventeenth century. From the late eighteenth to the early nineteenth centuries the Siamese, from their new capital at Bangkok, fought a series of wars with Champasak and Vientiane, eventually defeating these two Lao kingdoms and absorbing the Khorat Plateau and most of Laos as outer provinces within the Siamese kingdom. Luang Prabang became a tributary vassal of the Siamese kingdom. This situation changed with the arrival of the French in Indochina, beginning with their control of Cochin China in 1862. By 1904 Siam had ceded all of the Lao areas on the left bank of the Mekong River to France and established the boundary that exists between Thailand and Laos to the present day.
During most of the nineteenth century, Siam administered the northeast as tributary outer provinces. Local politics decided the rulers of those political units and the Siamese king only asked for tribute and allegiance. With the growth of colonial powers in the region, the Siamese kingdom sought closer control over the northeast and from the late nineteenth century on replaced local "lords" with government officials appointed from Bangkok.