The Thai people are of the Tai ethnic group, characterized by common linguistic roots. Chinese chronicles first mention the Tai peoples in the 6th century BCE. While there are many assumptions regarding the origin of Tai peoples, David K. Wyatt, a historian of Thailand, argued that their ancestors which at the present inhabit Laos, Thailand, Myanmar, India, and China came from the Điện Biên Phủ area between the 5th and the 8th century. Thai people began migrating into present-day Thailand around the 11th century, which Mon and Khmer people occupied at the time. Thus Thai culture was influenced by Indian, Mon, and Khmer cultures.
According to French historian George Cœdès, “The Thai first enter history of Farther India in the eleventh century with the mention of Syam slaves or prisoners of war in Champa epigraphy”, and “in the twelfth century, the bas-reliefs of Angkor Wat” where “a group of warriors” are described as Syam.
Early States and Sukhothai Kingdom:
According to the most widely accepted version of its origin, the Ayutthaya Kingdom rose from the earlier, nearby Lavo Kingdom and Suvarnabhumi with Uthong as its first king. Ayutthaya was a patchwork of self-governing principalities and tributary provinces owing allegiance to the King of Ayutthaya under the mandala system. Its initial expansion was through conquest and political marriage. Before the end of the 15th century, Ayutthaya invaded the Khmer Empire three times and sacked its capital Angkor. Ayutthaya then became a regional power in place of the Khmer. Constant interference of Sukhothai effectively made it a vassal state of Ayutthaya and it was finally incorporated into the kingdom. Borommatrailokkanat brought about bureaucratic reforms which lasted into the 20th century and created a system of social hierarchy called sakdina, where male commoners were conscripted as corvée labourers for six months a year. Ayutthaya was interested in the Malay peninsula, but failed to conquer the Malacca Sultanate which was supported by the Chinese Ming Dynasty.