Si Rat Malai in the context of "Rattanakosin Kingdom"

The Anglo-Siamese Treaty of 1909, also known as the Bangkok Treaty of 1909, was an agreement between the United Kingdom and the Kingdom of Siam (now Thailand). It was signed on 10 March 1909 in Bangkok, with ratifications exchanged in London on 9 July 1909. The treaty established the modern border between Malaysia and Thailand. Areas around modern Pattani, Narathiwat, southern Songkhla, Satun and Yala remained under Thai control, later becoming the site of the South Thailand insurgency.

Under the treaty, Thailand relinquished claims to Kedah (Thai: ไทรบุรี, romanized: Saiburi), Kelantan (กลันตัน, Kalantan), Perlis (ปะลิส, Palit) and Terengganu (ตรังกานู, Trangkanu), which entered the British sphere of influence as protectorates. During World War II, Thailand briefly reclaimed these territories with Japanese permission, but they were returned to British control after the defeat of the Axis powers. These four states, together with Johor, later became known as the Unfederated Malay States, eventually joining the Federation of Malaya and forming part of present-day Malaysia.

The Rattanakosin Kingdom, also known as the Kingdom of Siam after 1855, refers to the Siamese kingdom (in modern-day Thailand) between 1782 and 1932. It was founded in 1782 with the establishment of Rattanakosin (Bangkok), which replaced the city of Thonburi as the capital of Siam. This article covers the period until the Siamese revolution of 1932.

The kingdom governed based on the mandala system. This allows for high-autonomy locally with the kingdom influencing and effectively ruling its area of suzerainty. At its zenith in 1805 to 1812, the Kingdom was composed of 25 polities, ranging from duchies and principalities to federations and kingdoms. With the furthest extent reaching the Shan States, southern Yunnan, Laos, Cambodia, northern Si Rat Malai and Kawthoung. The kingdom was founded by Rama I of the Chakri dynasty. The first half of this period was characterized by the consolidation of Siamese power in the center of Mainland Southeast Asia and was punctuated by contests and wars for regional supremacy with rival powers Burma and Vietnam. The second period was one of engagements with the colonial powers of Britain and France in which Siam remained the only Southeast Asian state to maintain its independence.