Of European nations the Portuguese first established intercourse with Siam (i5i ). They were sup planted gradually in the 17th century by the Dutch. English trad ers were in Siam very early in the 17th century ; there was a friendly interchange of letters between James I. and the king of Siam, who had some Englishmen in his service, and, when the ships visited "Sia" (which was "as great a city as London") or the queen of Patani, they were hospitably received and accorded privileges. The important items of export were, as now, tin, varnish, deer skins and "precious drugs." Later on, the East India Company's servants, jealous at the employment of Englishmen not in their service, attacked the Siamese, which led to a massacre of the Eng lish at Mergui in 1687, and the factory at Ayuthia was abandoned in 1688. A similar attack is said to have been made in 1719 by the governor of Madras. After this the trade was neglected. Pulo Penang, an island belonging to the Siamese dependency of Kedah, was granted on a permanent lease to the East India Company in 1786, and treaties were entered into by the sultan of Kedah with the company. In 1822 John Crawfurd was sent to Bangkok to negotiate a treaty with the suzerain power, but the mission was unsuccessful. In 1824, by treaty with the Dutch, British interests became paramount in the Malay Peninsula and in Siam, and, two years later, Captain Burney signed the first treaty of friendship and commerce between England and Siam. A similar treaty was effected with America in 1833. Subsequently trade with British possessions revived, and in time a more elaborate treaty with England became desirable. Sir J. Brooke opened negotiations in 1850 which came to nothing, but in 1855 Sir J. Bowring signed a new treaty whereby Siam agreed to the appointment of a British consul in Bangkok, and to the exercise by that official of full extra territorial powers. Siam entered into treaties with Japan in 1898 and Russia in 1899. A further convention afterwards provided for a second British consular district in northern Siam, while England and France have both appointed vice-consuls in different parts of the country.
For centuries Siam had been dis tracted by wars with Cambodians, Peguans and Burmans, but the incorporation of Lower Cochin China, Annam and Tongking by the French, and the annexation of Lower and Upper Burma success ively by the British, freed her from all further danger on the part of her old rivals. But later, disputes with frontier tribes led to com plications with France, who asserted that the Siamese were occupy ing territory that rightfully belonged to Annam, which was now under French protection. France, while assuring the British Gov ernment that she laid no claim to the province of Luang Prabang, which was situated on both banks of the upper Mekong, roughly between the 18th and loth parallels, claimed that farther south the Mekong formed the true boundary between Siam and Annam, and demanded the evacuation of certain Siamese posts east of the river. The Siamese refused to yield, and early in 1893 encounters took place in the disputed area, in which a French officer was cap tured and French soldiers were killed. The French then despatched gunboats from Saigon to enforce their demands at Bangkok, and these made their way up to the capital in spite of an attempt on the part of the Siamese naval forces to bar their way. In conse quence of the resistance with which they had met, the French now greatly increased their demands, insisting on the Siamese giving up all territory east of the Mekong, including about half of Luang Prabang, on the payment of an indemnity and on the permanent withdrawal of all troops and police to a distance of 25 kilometres from the right bank of the Mekong. Ten days' blockade of the
port caused the Siamese government to accede to these demands, and a treaty was made, the French sending troops to occupy Chantabun until the provisions of this treaty should have been carried out.
In 1895 lengthy negotiations took place between France and England concerning their respective eastern and western frontiers in Farther India. These negotiations bore important fruit in the Anglo-French convention of 1896. By this convention Siam's independence was guaranteed by the two European powers who alone have interests in Indo-China. Encouraged by the assurance of the Anglo-French convention, Siam now turned her whole atten tion to internal reform, and to such good purpose that, in a few years, improved government and expansion of trade aroused a general interest in her welfare, and gave her a stability which had before been lacking. With the growth of confidence negotiations with France were reopened, and, after long discussion, the treaty of 1893 was set aside and Chantabun evacuated in return for the cession of the provinces of Bassac, Melupre, and the remainder of Luang Prabang, all on the right bank of the Mekong, and of the maritime district of Krat. These results were embodied in a new treaty signed and ratified in 1904.
Meanwhile, in 1899, negotiations with the British government led to agreements defining the status of British subjects in Siam, and fixing the frontier between southern Siam and the British Malay States, while in 1900 the provisions of Sir J. Bowring's treaty of 1855, fixing the rates of land revenue, were abrogated in order to facilitate Siamese financial reform.
In 1907 a further convention was made with France, Siam returning to the French protectorate of Cambodia the province of Battambang conquered in 1811, and in compensation receiving back from France the maritime province of Krat and the district of Dansai, which had been ceded in 1904. This convention also modified the extra-territorial rights enjoyed by France in Siam, and disclosed an inclination to recognize the material improve ments of the preceding years. In 1907 also negotiations were opened with Great Britain, the objects of which were to modify the extra-territorial rights conceded to that power by the treaty of 1855, and to remove various restrictions regarding taxation and general administration, which, though diminished from time to time by agreement, still continued to hamper the government. These negotiations resulted in a treaty, signed and ratified in 1909, by which Siam ceded to Great Britain her suzerain rights over the dependencies of Kedah, Kelantan, Trengganu and Perlis, Malay states situated in southern Siam just north of British Malaya, containing in all about a million inhabitants and for the most part flourishing and wealthy, and obtained the practical abolition of British jurisdiction in Siam proper.
In 1917 Siam declared war on Germany and Austria-Hungary. All enemy subjects were interned and a quantity of German ship ping taken as prize. The most important modern treaties are those made with the United States (1920) ; Japan (1924) ; Denmark, France, Holland, Portugal and Spain (1925) ; and in the same year a provisional economic arrangement was entered into with Ger many. In 1925, also, two new treaties (a new general and a new commercial treaty), were signed between Great Britain and Siam: they were ratified in May 1926. King Prajadhipok (b. 1893) suc ceeded his brother Rama VI. in Nov. 1925. In 1932 he pro claimed a limited monarchy; but in March 1935 he abdicated in favour of his nephew Ananda Mahidol (b. 1926).