This included imposing unified national language and cultural homogeneity across their territory, with centralized government, laws, administration. The other side of that is the suppression of regional languages and culture, as it happened during European nation-building with Welsh, Gaelic, Breton, Occitan, Alsatian, German and Italian dialects. Similarly in China, Japan, and elsewhere.
The building of telegraph lines, railways, and schools helped solidify nation state authority. I wonder how that relates to the internet, as a tool of communication as well as social control and centralizing power.
A way to summarize how Thailand resisted colonization is that it colonized itself, and successfully adapted culturally to the wave of Europeanization and modern global order of nation states.