Burmese–Siamese War (1765–1767)

The Burmese–Siamese War of 1765–1767, also known as the War of the Second Fall of Ayutthaya (Thai: สงครามคราวเสียกรุงศรีอยุธยาครั้งที่สอง) was the second military conflict between Burma under the Konbaung dynasty and Ayutthaya Kingdom under the Siamese Ban Phlu Luang dynasty that lasted from 1765 until 1767; the war ended the 417-year-old Ayutthaya Kingdom.

Burma under the new Konbaung dynasty emerged powerful in the mid-18th century. King Alaungpaya, the dynastic founder, led his Burmese forces of 40,000 men, and with his son Prince of Myedu as vanguard commander, invaded Siam in late 1759 to early 1760. The Burmese reached and attacked Ayutthaya in April 1760 but the arrival of rainy season and sudden illness of Alaungpaya prompted the Burmese to retreat. The traditional Siamese strategy of passive stand in the Ayutthaya citadel against Burmese besiegers worked for one last time, postponing the eventual fall of Ayutthaya for seven years. Alaungpaya died in May 1760 on his way from Siam back to Burma. Burmese invasion of Siam in 1760, in which the Burmese, particularly Prince Myedu, had an opportunity to learn about Siamese geography, strategy and tactics and to reflect about their own flaws in the campaign, served as the foundation of the next Burmese invasion in 1765–1767. Prince Myedu ascended the Burmese throne as King Hsinbyushin in late 1763. Hsinbyushin inherited military energy and prowess from his father Alaungpaya and was determined to accomplish his father's unfinished mission of conquering Ayutthaya.

Burma sent forces to successfully conquer Lanna Chiang Mai in 1762–1763.