Re: Thanks, Pol Pot
"The only exception to this rule was Thailand -- I don't know how they got away with it but they've always been independent."
They "got away with it" because they were lucky to have a progressive King (Mongkut[1]) who could see the way that the wind was blowing during the mid 19th C and who modernised Siam extremely quickly. He also realised that Westerners had many hang-ups over social conventions and modernised traditional Thai dress and customs to conform to Western expectations. Neighbouring countries that tried to preserve their customs were regarded by Westerners as "primitive" and therefore fit to be conquered by military means or by missionaries. Mongkut tamed both Western military and Western missionaries and adopted Western education in science and technology meaning that the Western powers largely left Siam alone because it was seen as "one of us."
A very clever and cunning man who also managed the royal succession extremely well, ensuring the continuity of the monarchy and the maintenance of Thai idependence.
[1] The King who features in "The King and I" musical.