The earliest mention of the Thai, as a nation in south China call NAN-JOA, comes from Chinese records dating back to the sixth century BCE. These early Thai emanated out of the Yunnan region and dispersed into the general area of what is today Thailand. These Thai peoples arrived in various waves and displaced the earlier native Mon and Khmer populations as they settled the region with a large group settling in Thailand during the Sung period of China roughly around 960 CE. The related Lao people split off from the early Tai-Kadai peoples and moved into Southeast Asia, mainly Laos, while another kindred people, the Shan, made their way into Myanmar.

The founding of the Sukhothai kingdom culminated in the emergence of the first Thai nation-state founded in 1238. Various conflicts in the Chinese-dominated region of Nanchao facilitated increased migration of the Thai, especially mercenaries fleeing from the Mongol conquest of China, and helped establish the Thai as a regional power. Successful wars with the Mon helped to establish the kingdom of Lan Na as the Thai increased their hold in Southeast Asia. The early Thai brought their Buddhist and Chinese traditions, but also assimilated much of the native Khmer and Mon culture of Southeast Asia. (See Thai Chinese for more details)

A new city-state known as Ayutthaya, named after the Indian city of Ayodhya, was founded by Ramathibodi (a descendant of Chiang Mai) and emerged as the center of the growing Thai Empire starting in 1350. Inspired by the then Hindu-based Khmer Empire (Cambodia), the Ayutthaya Empire's continued conquests led to more Thai settlements as the Khmer Empire weakened after their defeat at Angkor in 1444. During this period, the Thai developed a feudal system as various vassal states paid homage to the Thai kings. Even as Thai power expanded at the expense of the Mon and Khmer, the Thai Ayutthaya faced setbacks at the hands of the Malay at Malacca and were checked by the Toungoo of Burma.

Though sporadic wars continued with the Burmese and other neighbors, Chinese wars with Burma and European intervention elsewhere in Southeast Asia allowed the Thai to develop an independent course by trading with the Europeans as well as playing the major powers against each other in order to remain independent. The Chakkri dynasty under Rama I held the Burmese at bay, while Rama II and Rama III helped to shape much of Thai society, but also led to Thai setbacks as the Europeans moved into areas surrounding modern Thailand and curtailed any claims the Thai had over Cambodia, in dispute with Burma and Vietnam. The Thai learned from European traders and diplomats, while maintaining an independent course. Chinese, Malay, and British influences helped to further shape the Thai people who often assimilated foreign ideas, but managed to preserve much of their culture and resisted the European colonization that engulfed their neighbors.Thailand is also the only country that was not colonized in Southeastern Asia area in the early history