The Thai-Annamese War of 1831-1834, also known as the Siamese-Vietnamese pr Siamese-Cambodian War of 1831-1834, starts when Siam tries to conquer Cambodia but is repelled by Vietnam.

When Ang Chan II (1791-1837) became king of Cambodia in 1812, Siam had sent its forces into northern Cambodia and then southward, crushing the Cambodians at the Battle of Kompong Chang and forcing Ang Chan to escape to Vietnam in 1832.

The Siamese also threaten Vietnam, heading toward Chau Doc and Vinh Long before the Annamese counter-attack.

A rebellion breaks out in Cambodia and eastern Laos (under Siamese and Annamese control) and simultaneously a 15,000-man Annamese army advances against the Siamese (1833) and supports Ang Chan in arriving at Udong, the Cambodian capital (north of Phnom Penh).

With the retreat of the Siamese, Annam gains almost total control over Cambodia.