Phitsanulok in the context of Maha Thammaracha IV

The Burmese–Siamese War (1775–1776) or Maha Thiha Thura's Invasion of Siam or Athi Wungyi's War (Thai: สงครามอะแซหวุ่นกี้) was a major military conflict between the Konbaung dynasty of Burma (now Myanmar) and the Thonburi Kingdom of Siam (now Thailand).

After the Mon Rebellion of 1774 and the successful Siamese capture of Burmese-held Chiang Mai in 1775, King Hsinbyushin assigned Maha Thiha Thura the general of Sino-Burmese War to conduct a large-scale invasion of Northern Siam in late 1775 in order to curb the rising Siamese power under King Taksin of Thonburi. As the Burmese forces outnumbered the Siamese, the three-month siege of Phitsanulok was the main battle of the war. Defenders of Phitsanulok, led by Chaophraya Chakri and Chaophraya Surasi, resisted the Burmese. The war reached stalemate until Maha Thiha Thura decided to disrupt the Siamese supply line, leading to the Fall of Phitsanulok in March 1776. The Burmese gained upper hand but the untimely demise of King Hsinbyushin ruined the Burmese operations as the new Burmese king ordered the withdrawal of all troops back to Ava. The premature exit of Maha Thiha Thura from war in 1776 left the remaining Burmese troops in Siam to retreat in disarray. King Taksin then took this opportunity to send his generals to harass the retreating Burmese. The Burmese forces had completely left Siam by September 1776 and the war was over.