Dark ages of Cambodia

After a long series of wars with neighboring kingdoms, Angkor was sacked by the Ayutthaya Kingdom and abandoned in 1432 because of ecological failure and infrastructure breakdown. This led to a period of economic, social, and cultural stagnation when the kingdom's internal affairs came increasingly under the control of its neighbors. By this time, the Khmer penchant for monument building had ceased. Older faiths such as Mahayana Buddhism and the Hindu cult of the god-king had been supplanted by Theravada Buddhism.

The court moved the capital to Longvek where the kingdom sought to regain its glory through maritime trade. Portuguese and Spanish travelers described the city as a place of flourishing wealth and foreign trade. The attempt was short-lived however, as continued wars with the Ayutthaya and the Vietnamese resulted in the loss of more territory and Longvek being conquered in 1594. With the capturing of Longvek by the Siamese, the nation never fully recovered. During the next three centuries, the Khmer kingdom alternated as a vassal state of the Ayutthaya Kingdom and Vietnamese kings, as well as short-lived periods of relative independence.

A new Khmer capital was established at Udong south of Longvek, but its monarchs could survive only by entering into what amounted to vassal relationships with the Siamese and Vietnamese. A renewed struggle between Siam and Vietnam for control of Cambodia in the nineteenth century resulted in a period when Vietnamese officials attempted to force the Khmers to adopt Vietnamese customs. This led to several rebellions against the Vietnamese. The Siamese–Vietnamese War (1841–1845) ended with an agreement to placed the country under joint suzerainty. This later led to the signing of a treaty for French Protection of Cambodia by King Norodom I.