Siamese–Vietnamese War (1841–1845)
The 1841–1845 Siamese–Vietnamese War in Cambodia (, ) was a military conflict between the Nguyễn monarchy, ruled by Emperor Thiệu Trị, and the Kingdom of Siam, under the rule of Chakkri King Nangklao. The rivalry between Vietnam and Siam over the control of the Cambodian heartlands in the Lower Mekong basin had intensified after Siam had attempted to conquer Cambodia during the previous Siamese–Vietnamese War (1831–1834). Vietnamese Emperor Minh Mạng installed Princess Ang Mey to rule Cambodia as a puppet queen regnant of his choice in 1834 and declared full suzerainty over Cambodia, which he demoted to Vietnam's 32nd province, the "Western Commandery" (Tây Thành Province). In 1841, Siam seized the opportunity of discontent to aid the Khmer revolt against Vietnamese rule. King Rama III sent an army to enforce Prince Ang Duong's installation as King of Cambodia. After four years of attrition warfare, both parties agreed to compromise and placed Cambodia under joint rule.