Two groups of Khmer could also be distinguished--long-time inhabitants of Thailand and more recent arrivals. By the midfifteenth century, much of the western region of the Khmer Empire had come under the control of Ayutthaya. Many of the Khmer peoples remained in the area that had come under Thai domination. Five centuries later the protracted civil conflict in Cambodia, which began with the overthrow of the Lon Nol regime in 1975 and included the Vietnam-supported overthrow of the Pol Pot regime in 1979, led to the arrival at the Thai-Cambodian border of additional hundreds of thousands of Khmer. Some Khmer had crossed over into Thailand many others might be expected to do so if several political obstacles were overcome (see The Indochinese Refugee Question , this ch. Potential External Threats , ch. 5).

Theravada Buddhists and wet-rice cultivators, the Khmer spoke a language of the Mon-Khmer group and were heirs to a long and complex political and cultural tradition. If long-term resident Khmer and Khmer refugees were both included, there were perhaps as many as 600,000 to 800,000 Khmer living in Thailand in the 1980s. Many of the long-resident Khmer were said to speak Thai, sometimes as a first language, and religious and other similarities contributed over time to Thai-Khmer intermarriage and to Khmer assimilation into Thai society. Newly arrived Khmer, however, were not yet assimilated.

Data as of September 1987