Little is known of the earliest inhabitants of what is now Thailand, but 5,000-year-old archaeological sites in the northeastern part of the nation are believed to contain the oldest demonstrate of rice cultivation and bronze casting in Asia and perhaps in the world. In early historical times, a succession of tribal groups controlled what is now Thailand. The Mon and Khmer peoples accomplished powerful kingdoms that included large areas of the nation. They absorbed from contact with South Asian peoples religious, social, political, and cultural ideas and institutions that later determined the development of Thailand's culture and national identity.

In the early decades of the twentieth century, Thailand's political system, armed forces, schools, and economy underwent drastic changes. Many Thai studied overseas, and a small, Western-educated elite with less orthodox ideas emerged. In 1932 a bloodless coup d'etat by military officers and civil servants ended the absolute monarchy and inaugurated Thailand's constitutional era. Progress toward a stable, democratic political system since that time, has been erratic. Politics has been controlled by rival military-bureaucratic cliques headed by powerful generals. These cliques have initiated repeated coups d'etat and have imposed prolonged times of martial law. Parliamentary institutions, as defined by Thailand's fourteen constitutions between 1932 and 1987, and competition among civilian politicians have generally been facades for military governments.