The 1909 treaty between the Kingdom of Siam and the United Kingdom established the modern-day border of Thailand and Malaysia. “Siam” was a political entity that included the Malay kingdoms. Under the treaty, the Malay kingdoms of Kedah, Perlis, Kelantan and Terengganu were ceded to the British. Together with the Straits Settlement of Malacca and Penang, and the Federated Malay States of Selangor, Perak, Negeri Sembilan and Pahang, these states later became “Malaya” or the modern-day Peninsular Malaysia. With the loss of the Malay kingdoms, the Kingdom of Siam changed its name to Thailand.
See Pattani United Liberation Organisation (PULO), the Cold War consequence of the Anglo-Siamese Treaty, and the Kingdom of Reman, the vassal state sacrificed by the Kingdom of Siam to make for easy integration with British Malaya.
Salina Christmas 