The Thai government has since the late 19th century tried to achieve the national integration through various policies. These were, however, often carried out without consideration for the culture and interests of the peoples in the provinces of the South, Northeast and North. The result was that Thai society has experienced regional and ethnic conflicts in these three outlying regions. The reasons of the conflicts can be analysed from not only a primordial but a circumstantial perspective. For the latter's viewpoint, the following factors of internal colonialism will be discussed: the introduction of the centralized administration and education and the intensification of the Thai nationalism since the late 19th century, and the industrialization policy centering on Bangkok and central region since the 1950s.