Given the question: Question: "What happened in the 19th century?"  Context: "With Burma preoccupied by the Chinese threat, Ayutthaya recovered its territories by 1770, and went on to capture Lan Na by 1776. Burma and Siam went to war until 1855, but all resulted in a stalemate, exchanging Tenasserim (to Burma) and Lan Na (to Ayutthaya). Faced with a powerful China and a resurgent Ayutthaya in the east, King Bodawpaya turned west, acquiring Arakan (1785), Manipur (1814) and Assam (1817). It was the second-largest empire in Burmese history but also one with a long ill-defined border with British India."  Answer:
The answer is:
Burma and Siam went to war