We only say that the Tai-Lao came from Yunnan, China via Eastern China. This is true. The indignous people of Siam are Mon-Khmer who settled in this region for thousands of years and already built a great civilization and culture before the arrivals of the Tai tribes. Thailand would have been develop by now if they didn't have over 45 million Tai people holding the country back from moving forward. I understand why Thai government change the culture and language to sound more Tai-Kradai because the Tai population was very large and tribalistic. So in order to unite them together they created a centralize and standard Thai language mixing all cultures into one.
@imperialkhmer6146 Khmer comes from the forest people of Indonesia. Can be seen from the DNA test results. which does not match the DNA of the people in this area
There is no central authority for the Dvaravati kingdoms because they lack road systems to connect people, culture, administration, laws, language, and such. This is where the Khmers came and built roads, bridges, headquarters, tax offices, and such to control far flung areas under Angkor central administration. The Tai kingdoms, Burmese kingdoms, Champa kingdoms, Viet kingdoms, Malay kingdoms, and such never built roads which is the main core of centralization.