The term isan has been said to mean "northeast" in the Thai language. Isan has a number of important Bronze Age sites, with cliff paintings, artifacts and early evidence of rice cultivation. Iron and bronze tools, such as found at Ban Chiang, may predate similar tools from Mesopotamia. The region later came under the influence of the Dvaravati culture, followed by the Khmer empire. The latter built dozens of prasats (sanctuaries) throughout the Isan region; the most significant are at Phimai and Phanom Rung.
After the Khmer empire began to decline from the 13th century, Isan was dominated by the Lao Lan Xang kingdom, which had been established by Fa Ngum. The region was increasingly settled by Lao and Thai migrants. Siam held sway from the 17th century, and carried out forced population transfers from Laos to Isan in the 18th and 19th centuries. Franco-Siamese treaties of 1893 and 1904 made Isan the frontier between Siam and French Indochina.
In the 20th century, a policy of nationalist "Thaification" promoted the incorporation of Isan as an integral part of Thailand and de-emphasised the Lao and Khmer ethnicities of the residents. The national government claimed (incorrectly) that the name "Isan" was derived from that of Iśāna (Sanskrit: ईशान), a manifestation of Shiva as deity of the northeast, and the Sanskrit word for northeast. This interpretation was intended to reinforce the area's identity as the northeast of Thailand, rather than as a part of the Lao world. But, the name was used during the period when the territory of modern-day Thailand was ruled by the Mon and Khmer kingdoms. It predates any Thai or Lao populations. The name does not refer to the "north east"; it refers to "invisible power" and is derived from the area's pre-Thai and pre-Angkorian history.
Before the central government introduced the Thai alphabet and language in regional schools, the people of Isan wrote in the Lao alphabet, a similar script. Most Isan people still speak the Isan language, a dialect of the Lao language. A significant minority also speak Northern Khmer. The Kuy people, who are concentrated around the core of the Isanapura kingdom, and known as "Khmer Boran" or ancient Khmer, speak other Katuic languages, a link to the region's pre-Siamese history as part of the Mon–Khmer kingdom of Chenla.
