1824, Jul 20 - King Rama II dies at 57, without having appointed a heir to the throne (in spite of the fact that he had 38 male and 35 female children from 38 different mothers). With the consent of the Accession Council (comprised mainly of members of the royal family) Prince Jetta, the eldest son of Rama II but begotten with a non-royal wife succeeds the throne - instead of Prince Maha Mongkut, the eldest son of the King by a royal mother who could have been considered the rightful successor to the King. But due to Prince Maha Mongkut’s exposure and prominent participation in numerous public affairs, Prince Jetta wins the support of the Accession Council so that no opposition comes up during his proclamation as King Rama III. His posthumous title is Phra Nangklao.
1826 - A treaty of friendship and commerce is concluded between Siam and the British East India Company (against which the Siamese King Narai had declared war more than 100 years before).
1833 - Siam concludes its first treaty of amity and commerce with the US.
1838 - The former Sultan of Kedah tries to regain control of his territory. Siam invades Kedah again, affecting the nearby Malay territories which had already been accepted as belonging to Great Britain thus straining the relationship between Siam and Great Britain.
1851, Apr 2 - Upon the death of his half brother, King Rama III, Prince Maha Mongkut is finally crowned King Rama IV, assuming the royal title Phra Chomklao. After missing out on the throne in 1824, he had become a Buddhist monk for 27 years and lived a highly disciplined live in northern Siam. He even founded the monastic sect Thammayut which still exists and whose rules are stricter than those of the larger Mahanikai sect. During his monastic life, he studied Western science as well as Western and Eastern languages. With this background he intends to open Siam to the west. The opening brought about by Mongkut probably saves the Thai kingdom from becoming a colony of either Britain or France. By making concessions and by and large granting the European powers what they think they urgently need, he avoids his kingdom becoming a target for European conquest. One of the main matters, Mongkut has to grant the European powers are rights on free trade.
1852 - The 2nd Anglo-Burmese war breaks out. The rest of the southern provinces of Burma (with Pegu being the most important) are annexed to the British Empire. Siam still maintains neutrality.
1855, Apr 18 - By virtue of a treaty between Siam and Great Britain, a consular jurisdiction is established in Siam; residences of British subjects become restricted, extraterritorial areas; import duties are lowered. This agreement follows a pattern imposed by European powers through force on many east Asian countries.
1856, Apr 15 - Through Townsend Harris, the US begins negotiating with Siam to amend their 1833 treaty (the amendments should be of advantage for the US).
1856, May 29 - The new Treaty of Amity, Commerce and Immigration is concluded between the US and Siam. Stephen Mathon is sent as the first US consul to Bangkok.
1862 - Construction of a more advanced infrastructure system begins; it concentrates on roads (transportation so far had been mainly on canals). Most significant is the construction of Charoen Krung or New Road along the Chao Phaya River in Bangkok.
1863, Aug 11 - Cambodia though in the preceding decades a vassal of Siam becomes a French protectorate by virtue of a treaty concluded between Cambodian King Norodom and France.
1867, Jul 15 - Siam stops collecting taxes and tribute from Cambodia, recognizes the country as a French protectorate and annuls all earlier treaties between Siam and Cambodia. However, (for the time being) the Cambodian provinces of Battambang and Seemap bordering Thailand are excepted and recognized as belonging to Siam.
