Modern historians stated that the secession of Sukhothai from the Khmer empire began as early as 1180 during the reign of Po Khun the ruler of Sukhothai and the peripheral city of Sri Satchanalai. Sukhothai had enjoyed a substantial autonomy until it was re-conquered around 1180 by the Mons of Lavo under Khomsabad Khlonlampong. Two brothers, Po Khun Bangklanghao and Po Khun Phameung (Po KhAt the end of his reign in 1257, the Sukhothai kingdom covered the entire Upper Chao Phraya valley.
Traditional Thai historians considered the foundation of the Sukhothai kingdom as the beginning of their nation because little was known about the kingdoms prior to Sukhothai. Modern historical studies demonstrate that Thai history began before Sukhothai. Yet the foundation of Sukhothai is still a celebrated event
un was a Siamese title of high nobility) took Sukhothai from Mon hands in 1239