The Foundation of Sukhothai
Scholars have suggested that Sukhothai was previous ruled by Pho Khun Sri Now Num Thom. When this ruler passed away Khom Sabaad Khlone Lamphong, identified by historians as a Khmer officer who had been sent to take care of the religious sanctuary in Sukhothai, took over the Sukhothai and Sri Satchanalai cities. Later, Pho Khun Pha Muang, a son of Pho Khun Sri Now Num Thom, cooperated with Pho Khun Bang Klang How, the ruler of Bang Yang town, attacked and finally defeated the Khmer officer. Pho Khun Bang Klang How was appointed as a new king of Sukhothai and was named Pho Khun Sri Indrathit. When the king Sri Indrathit passed away, his son named Pho Khun Ban Muang took over the power. Later, Pho Khun Ramkhamhaeng, a younger brother of Pho Khun Ban Muang, took the throne when his brother passed away. King Ramkamhaeng was a great warriors and could largely extend the area under his ruling.
Lanna retained a considerable measure of autonomy until the 18th century, and Chiang Mai, which became the permanent capital after 1339, is still a major centre of northern Thai culture as well as being the second city of Thailand. In the mid 13th century, as Khmer power in central Thailand waned, the Thais moved further south to the headwaters of the Chao Phraya River, where at some time in the 1240s a Thai chief named Bang Klang Hao rebelled successfully against his Khmer rulers and was crowned King Sri Indraditya of Sukhothai. The new Thai state of Sukhothai is referred to by the Chinese of the late 13th century as Siem (Siam), a name that occurs in earlier Cham, Khmer and Burmese inscriptions, where it denotes Tai slaves and mercenary soldiers.
Sukhothai, meaning the ''Dawn of Happiness'' was the first free Thai city founded in 1238, by two Thai chieftains, Khun Bang Klang Tao and Khun Pa Muang , this ending Khmer rule from Angkor Wat. In the early 1300s, Sukhothai enjoyed suzeranity over the Chao Phya River basin, westward to the bay of Bengal and the entire Peninsula. It is still regarded by Thai historical tradition as the " first Thai Kingdom " , it began life as a chiefdom under the sway of the Khmer empire: the oldest monuments in the city were built in the Khmer style or else show clear Khmer influence.
During the first half of the 13th century the Thai rulers of Sukhothai threw off the Khmer yoke and set up an independent Thai kingdom. One of the victorious Thai chieftains became the first king of Sukhothai, with the name of Si Inthrathit [Sri Indraditya]. Sukhothai's power and influence expanded in all directions by conquest [the Khmer were driven southwards], by a farsighted network of marriage alliances with the ruling families of other Thai states, and by the use of a common religion, Theravada Buddhism, to cement relations with other states.