Burmese–Siamese War (1849–1855)

An 1803-1808 war over territory resulted in a successful Burmese defense of Sipsongpanna and Kengtung. However, the Burmese failed to retake Chiang Saen, and the war largely ended in a stalemate. However, the Siamese kept their claims over the trans-Salween region and waited for an opportunity to regain these lands.

Their opportunity arrived in the early 19th century, as the Burmese Empire was weakened by war with the British and the Qing Empire, the most powerful and most populous sovereign powers in the world. The Burmese kingdom, and even Burmese sovereignty were under threat. The Qing built up military forces on their border with Burma, and British ambition resulted in a campaign for influence that would soon result in British occupation of lower Burma.

As the Burmese army under Mindon Min, the penultimate Burmese king, was primarily occupied keeping the British and Qing at bay, the Siamese under King Rama III saw an opportunity to invade and capture Burmese territory. Increasing unrest in the Shan minority (an ethnic group related to the Thai people)-populated Kengtung and Chiang Hung state due to weakening Burmese power provided an impetus for invasion.

Siamese forces began to raid Burmese settlements around the city of Kengtung beginning in 1849, testing Burmese sovereign strength. King Rama III of Thailand died in 1851, leaving the task of taking Kengtung to his successor, Rama IV. After encountering minimal resistance during the raids, the Siamese sent two invading forces in 1852 from Chiang Mai. Notably, even in the 19th century, the invading force included war elephants and light artillery.[2]

As Mindon was still in fear of a British invasion, he only sent a few thousand infantry to combat the Siamese, who were now laying siege to Kengtung. After suffering heavy losses, the Burmese were finally able to drive the Siamese out. However, in 1854, the Siamese returned with an even larger force, consisting of Siamese and conscripted Lao forces.

However, the Burmese army was ready for invasion this time, due to the end of the Second Anglo-Burmese War that had formerly been keeping them occupied.[3] The Burmese were also now better equipped, with an artillery corps and over 3,000 cavalrymen, as part of Mindon's modernization program. Despite this, the Siamese army persevered, again reaching Kengtung. However, faced with harsh mountainous terrain and a lack of resources, the Siamese were driven back for good in May 1855.

King Rama III's untimely death on 2 April 1851 occurred in the midst of the war. Some of his final words were advice to his country to cease its conflicts with neighboring Southeast Asian states and focus on the threat of European colonialism.

Our wars with Burma and Vietnam were over, only the threats of the Westerners [are] left to us. We should study their innovations for our own benefits but not to the degree of obsession or worship.

— King Rama III

His words did not stop the war, but proved to be prophetic. After major intervention in Southeast Asia by Europeans in the late 19th century, the thousand-year-old Burmese empire fell to the British, nearby Vietnam fell to the French,[4] and Thailand remained the only Southeast Asian country not colonized by Europeans, but only after ceding around half of its territory to European powers.

• Burmese–Siamese wars
• Burma–Thailand relations