The Anglo-Siamese Treaty of 1909, signed between the United Kingdom and the Kingdom of Siam, established the modern Malaysia–Thailand border. Thailand retained control over areas like Pattani, Narathiwat, and Yala but ceded sovereignty over Kedah, Kelantan, Perlis, and Terengganu to the British, which later became part of the Unfederated Malay States. Historically, Siam's monarchs, starting with Rama I, worked strategically to maintain the nation's independence, often through treaties and concessions with foreign powers. Significant treaties, like the Burney Treaty and the Bowring Treaty, marked Siam's interactions with the British, ensuring trade privileges and affirming territorial rights, all while modernizing rulers like Chulalongkorn made reforms to centralize and modernize the nation.