The present-day boundary of southern Shan State vis-à-vis Thailand was formed shortly thereafter. Burma lost southern Lan Na (Chiang Mai) in 1776 and northern Lan Na (Chiang Saen) in 1786 to a resurgent Bangkok-based Siam, ending more than two centuries of Burmese suzerainty over the region. It retained only Kengtung on the Burmese side. The southern border of Shan State remained contested in the following years. Siam invaded Kengtung in 1803–1804 and 1852–1854, and Burma invaded Lan Na in 1797 and 1804. Siam occupied Kengtung during World War II (1942–1945).