…Indravarman’s Thai subjects rebel, establish the first Thai kingdom at Sukhothai, and push back the Khmer.

The Tais, or Thais, wet rice cultivators who began migrating into the watery Chao Phraya basin from south China in the eleventh century to exploit the region’s agricultural potential, establish the state of Sukhothai (“Dawn of Happiness”) under Khmer suzerainty.

Tai kingdoms had existed prior to the thirteenth century, on the northern highlands including the Ngoenyang (centered on Chiang Saen; predecessor of Lanna) kingdom and the Heokam (centered on Chiang Hung, modern Jinghong in China) kingdom of the Tai Lue people.

Sukhothai had been a trade center and part of Lavo, which was under the domination of the Khmer Empire.

The migration of Tai people into upper Chao Phraya valley was somewhat gradual.

Modern historians state that the secession of Sukhothai from the Khmer empire began as early as 1180 during the reign of Po Khun Sri Naw Namthom, who was the ruler of Sukhothai and the peripheral city of Sri Satchanalai (now a part of Sukhothai Province as Amphoe).

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 Khun is a Siamese title of high nobility), the Thai governors of, respectively, Ban Yang and Rad, had rebelled against Khmer rule in 1238 to overpower the Mon kingdom of Dvaravati.

The brothers take Sukhothai, since the eleventh century a viceroyalty under the Khmer Empire, from Mon hands and in 1239 establish the Thais’ first truly independent kingdom in Sukhothai.

Bangklanghao rules Sukhothai as Sri Indraditya and begins the Phra Ruang Dynasty, soon expanding his primordial kingdom to the bordering cities.

In the following two hundred years, the Thais will become the chief rivals of the Khmer state.