Siam (modern day Thailand) which since the late eighteenth century royal investiture of General Chakri was governed by a well established dynasty and Vietnam united since 1802 under Emperor Gia Long increasingly fought over control of the fertile Mekong basin, the Cambodian heartland. Siam had after the 1594 conquest of Cambodia's capital Longvek and the permanent annexation of Cambodia's Battambang and Siem Reap provinces introduced a tradition of taking Cambodian royalty hostage and relocate them at the court of Ayutthaya. Thus, Siam effectively controlled Cambodian national policies and royal succession. After initially conquering all of Cambodia during the Siamese–Vietnamese War of 1831 to 1834, Siam, attempting to conquer Southern Vietnam was defeated by Vietnamese troops and pushed back. Vietnam subsequently gained military control of Cambodia and restored King Ang Chan, who had been dethroned by Siam. Only a decade later Khmer discontent with increasing Vietnamese dominance among demands to adopt Vietnamese customs encouraged Siam to intervene and invade again during the Siamese–Vietnamese War of 1841 to 1845. Again Vietnam proved to be superior on the battlefield, however Siam was able to negotiate an agreeable peace treaty, by which Cambodia was placed under joint Siamese-Vietnamese suzerainty, a final act of complete disregard for Khmer national and royal authority.
