The Burmese–Siamese War (1785–1786), known as the Nine Armies' Wars in Siamese history because the Burmese came in nine armies, was fought between the Konbaung dynasty of Burma and the Chakri dynasty of resurgent Siam (Thailand).
In early 1785, King Bodawpaya of Konbaung dynasty sent an expedition force to take Jung Ceylon (Phuket) to prevent foreign arms shipments to Siam but the invasion force was driven back. In October 1785, Bodawpaya pursued an ambitious campaign to expand his dominions into the lands of the former Ayutthaya Kingdom. He launched a four-pronged invasion towards Chiang Mai, Tak, Kanchanaburi, and Jung Ceylon. The combined strength was about 50,000 men. The invasion forces had faced tough heavy resistance from the Siamese forces and finally the war become a total disaster of the Burmese armies. The defeat that the invasion turned out to be the last full-scale invasion of Siam by Burma.