British relations with Thailand date back to 1612, when the East India Company ship The Globe arrived in Siam carrying a letter from King James I for the Siamese king.[56] Conflicts with the East India Company during the reign of Ayutthayan King Narai resulted in the Siam–England war of 1687, after which the English were banned from Siam.[57] After Burma lost the First Anglo-Burmese War (1824–26) relations opened between the Rattanakosin Kingdom of Siam and the United Kingdom with a treaty of alliance in February 1826 and another treaty in June negotiated by East India Company emissary Henry Burney. This was followed by the Bowring Treaty of 1855 to liberalise trade. In 1893, Lord Lansdowne of the British Raj finalized the border between Burma and Siam; the Anglo-Siamese Treaty of 1909 then dissected the northern Malay states.
In 1917 the modern Siamese kingdom declared war on Germany during World War I, which secured it a seat at the Versailles Peace Conference. Foreign Minister Devawongse Varopakarn used this as an opportunity to argue for the repeal of the 19th century treaties and restoration of full Siamese sovereignty. While Britain and France delayed until 1925, the United States obliged in 1920. Following the outbreak of World War II, relations with Britain, France and the United States deteriorated rapidly – though former Queen Rambai Barni was nominal head of the Seri Thai resistance movement in Great Britain. Japan allowed Thailand to resume sovereignty over the sultanates of northern Malaya that had been lost in the 1909 treaty with Britain, and to invade and annex the Shan States in northern Burma. After the Japanese surrender, Allied military responsibility for Thailand fell to the British, who favoured treating the kingdom as a defeated enemy. Americans, however, supported Thailand's new government; during the Cold War relations with the United Kingdom took a back seat to those with the United States.