Enlightenment
Mongkut came to the throne as Rama IV in 1851, determined to save Siam from colonial domination by forcing modernisation on his reluctant subjects. But although he was in theory an absolute monarch, his power was limited. Having been a monk for 27 years, he lacked a base among the powerful royal princes, and did not have a modern state apparatus to carry out his wishes. His first attempts at reform, to establish a modern system of administration and to improve the status of debt-slaves and women, were frustrated.
Rama IV thus came to welcome western intrusion in Siam. Indeed the king himself and his entourages were actively pro-British. This came in 1855 in the form of a mission led by the Governor of Hong Kong, Sir John Bowring, who arrived in Bangkok with demands for immediate changes, backed by the threat of force. The King readily agreed to his demand for a new treaty, called the Bowring Treaty, which restricted import duties to 3%, abolished royal trade monopolies, and granted extraterritoriality to British subjects. Other western powers soon demanded and got similar concessions.
The king soon came to consider that the real threat to Siam came from the French, not the British. The British were interested in commercial advantage, the French in building a colonial empire. They occupied Saigon in 1859, and 1867 established a protectorate over southern Vietnam and eastern Cambodia. Rama IV hoped that the British would defend Siam if he gave them the economic concessions they demanded. In the next reign this would prove to be an illusion, but it is true that the British saw Siam as a useful buffer state between British Burma and French Indochina.
Read more about this topic: Rattanakosin Kingdom