What happened
Negotiated by Sir John Bowring, Governor of Hong Kong, the treaty was signed on April 18, 1855. Import duties were capped at 3 percent, crown trade monopolies were ended for British traders, and British subjects gained the right to trade and reside in Bangkok with extraterritoriality. Rice export was also permitted.
Background
After the Opium War, Western pressure on Asian states was unmistakable; the earlier Burney Treaty (1826) had given only limited access. Mongkut, watching the fates of China and Burma, is commonly assessed to have chosen negotiation over confrontation.
Consequences
Parallel treaties with the United States, France and other powers followed on the same model. Siam integrated into the world economy: rice exports and Bangkok’s trade boomed. The treaty’s unequal features — extraterritoriality and the tariff cap — were revised away only in the early 20th century, and fully by the late 1930s. The treaty is often credited as a key step in how Siam kept its independence.