The Siamese–Vietnamese War of 1841–1845 (Thai: อานามสยามยุทธ (พ.ศ. 2384 – พ.ศ. 2388), Vietnamese: Chiến tranh Việt–Xiêm (1841–1845)) was a military conflict between the Đại Nam, 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 disconte