Sukhothai kingdom
The city of Sukhothai was part of the great Khmer empire until 1238, when two Thai chieftains, Pho Khun Pha Muang and Pho Khun Bang Klang Hao, declared their independence and established a Thai-ruled kingdom. Pho Khun Bang Klang Hao later became the first king of Sukhothai, calling himself Pho Khun Si Indrathit (or Intradit). This event traditionally marks the founding of the modern Thai nation, although other less well-known Thai kingdoms, such as Lanna, Phayao and Chiang Saen, were established around the same time.
Sukhothai expanded by forming alliances with the other Thai kingdoms, adopting Theravada Buddhism as the state religion with the help of Ceylonese monks. Intradit was succeeded by his son Pho Khun Ban Muang, who was followed in 1278 by his brother, Pho Khun Ramkhamhaeng. Under King Ramkhamhaeng the Great, as he is now known, Sukhothai enjoyed a golden age of prosperity. Ramkhamhaeng is credited with designing the Thai alphabet (traditionally dated from 1283, on the evidence of the controversial Ramkhamhaeng stele, an inscribed stone allegedly bearing the earliest known Thai writing). At its peak, supposedly stretching from Martaban (now in Burma) to Luang Prabang (now in Laos) and down the Malay Peninsula as far south as Nakhon Si Thammarat, the kingdom's sphere of influence was larger than that of modern Thailand, although the degree of control exercised over outlying areas was variable.