Northern Khmer (; ), also called Surin Khmer (), is the dialect of the Khmer language spoken by approximately 1.4 million Khmers native to the Thai provinces of Surin, Sisaket, Buriram and Roi Et as well as those that have migrated from this region into Cambodia. Northern Khmer differs from the standard language, based on a dialect of Central Khmer, in the number and variety of vowel phonemes, consonantal distribution, lexicon, grammar, and, most notably, pronunciation of syllable-final , giving Northern Khmer a distinct accent easily recognizable by speakers of other dialects. Some speakers of Northern Khmer may understand other varieties of Khmer but speakers of standard Khmer who have not been exposed to Northern Khmer often have trouble understanding Northern Khmer at first. The two varieties are 80–85% cognate on a basic 270-word list. These facts have led some linguists to advocate considering Northern Khmer a separate, but closely related language. History After the fall of the Khmer Empire in the early 15th century the Dongrek Mountains served as a natural border, leaving the Khmer north of the mountains increasingly under the sphere of influence of Lan Xang. The conquests of Cambodia by Naresuan the Great for Ayutthaya furthered the political and economic isolation from Cambodia proper, leading to a dialect that developed relatively independently from the midpoint of the Middle Khmer period. Subsequently, the Isan area was claimed by the Lao Kingdom of Champasak in 1718 and in 1893, the region became part of the Kingdom of Siam (Thailand) as a result of the Franco-Siamese War. Throughout this period, the Northern Khmer people shared the rural mountainous highlands with the Lao, Thai and various Mon-Khmer groups such as the Kuy, leading to a high degree of multilingualism. These varied influences and unique history have resulted in a distinct accent, with characteristics of the surrounding tonal languages, lexical differences through borrowing from Lao, Kuy and Thai, and phonemic differences in both vowels and distribution of consonants. Status Most, or probably all, speakers of Northern Khmer are bilingual, being also proficient in the national language Thai, which is the sole language of education and mass communication. Usage of Northern Khmer is restricted to the domestic and village domain. In the past, its use was actively disfavored (e.g. by prohibiting speaking Northern Khmer in school classrooms) to boost proficiency in the national language. Only a few (c. 1,000) speakers of Northern