How Thailand Resisted Colonization

It depends whether one considers Thailand to have been part of informal empire or not, much like the British influence over Portugal, Chile and Argentina.

Either way, Thailand was also a Cold War hold out. It bordered Cambodia, Laos and Burma, and Vietnam by sea, all of which became Communist-run. The west helped prop it up.

There is a whole other argument about Thailand's current relationship with the west, which is complex to say the least.