[snorter]

LivinLOs: I heard that Burma extends as far south as it does in that the Brits made a deal to Leave Thailand alone as long as they were given enough to be able to steam in one passage from colonial burma to colonial penang.

Mr Lucky: ........... that's the deal in which Thailand ended up gaining the southern provinces from Malaysia. The British made a trade - a bit of Malaysia in exchange for a strip of Thailand. That's why some southerners feel they don't belong to Thailand.

snorter: Thailand actually lost territories to Britain in the south. The Siamese tributaries of Perlis, Kedah, Kelantan and Trengganu were ceded to Britain in 1909 and remain today outside Thai territory.

And from wikipedia: "The Anglo-Siamese Treaty of 1909 made the modern border between Siam and British Malaya by securing the Thai authority onthe provinces of Pattani, Yala, Narathiwat and Satun, which were previously part of the semi-independent Malay sultanates of Pattani and Kedah. A series of treaties with France fixed the country's current eastern border with Laos and Cambodia."



Above comments cover a very subjective period in Thai History, a bit like History being written by the victor, I think it's all about perspective; The Brits at the time felt the territory belonged to no-one and was up for grabs, the Siamese felt it was under their scope of influence and the local populace felt it was free but with trading ties to both Malaysia and Siam.
Wikipedia says: they were part of the semi-independent Malay sultanates. What you have to bear in mind is that, at the time, all of what is now called Thailand was semi-independent of the Siamese in the Chaophraya basin.

Also from wikipedia: "Additionally tributary states like the principalities of Lannathai, the Laotian kingdoms of Vientiane and Luang Prabang, Cambodia, or the Malay sultanate Kedah were also part of the country, but with an
even higher autonomy than the provinces. In this Mandala system the semi-independent countries sometimes were tributary to more than one country."

At the time Lannathai was Chiang Mai area, Vientiane incorporated Nong Khai, Udon Thani, Nakhom Phanom and the Khmer tributary included the Khorat plateau.