The Thai have traditionally regarded the founding of the kingdom of Sukhothai as marking their emergence as a distinct nation. Tradition sets 1238 as the date when Tai chieftains overthrew the Khmer at Sukhothai, capital of Angkor's outlying northwestern province, and established a Tai kingdom. A flood of migration resulting from Kublai Khan's conquest of Nanchao furthered the consolidation of independent Tai states. Tai warriors, fleeing the Mongol invaders, reinforced Sukhothai against the Khmer, ensuring its supremacy in the central plain. In the north, other Tai war parties conquered the old Mon state of Haripunjaya and in 1296 founded the kingdom of Lan Na with its capital at Chiang Mai.
Situated on the banks of the Mae Nam Yom some 375 kilometers north of present-day Bangkok, Sukhothai was the cradle of Thai civilization, the place where its institutions and culture first developed. Indeed, it was there in the late thirteenth century that the people of the central plain, lately freed from Khmer rule, took the name Thai, meaning "free," to set themselves apart from other Tai speakers still under foreign rule.
The Sukhothai of small villages scattered along the Yom and the Nan River basins formed in AD 1157. During that time these villages prospered from the expansion of interstate transport and trade to the extent that they finally amalgamated and established their own territory. Sukhothai was governed in the style of "the Father of the Town," or paternal kingship, and was ruled by nine consecutive kings. This kingdom lasted approximately two centuries from its inception until it was merged with the Ayutthaya Kingdom.
The current concept of Thai kingship has evolved through 800 years of absolute rule. The first King of a unified Thailand was the founder of the Kingdom of Sukhothai: King Sri Indraditya in 1238. During his reign the kingdom was extended by amalgamation with other towns. The next most significant was the second son of King Si Inthrathit, King Ram-khamhaeng, the third king, who was also the most renowned of the Sukhothai monarchs. Ram-khamhaeng (Rama the Great, 1277-1317) was the first ruler of Sukhothai for whom historical records survive. He was a famous warrior who claimed to be "sovereign lord of all the Tai" and financed his court with war booty and tribute from vassal states in Burma, Laos, and the Malay Peninsula. During his reign, the Thai established diplomatic relations with China and acknowledged the Chinese emperor as nominal overlord of the Thai kingdom. Ramkhamhaeng brought Chinese artisans to Sukhothai to develop the ceramics industry that was a mainstay of the Thai economy for 500 years.