The Khmer Empire was an empire in mainland Southeast Asia, centered on hydraulic cities in what is now northern Cambodia. Known as Kambuja (Old Khmer: កម្វុជ; Khmer: កម្ពុជ) by its inhabitants, it grew out of the former civilization of Chenla and lasted from 802 to 1431. Historians call this period of Cambodian history the Angkor period, after the empire's most well-known capital, Angkor. The Khmer Empire ruled or vassalised most of Mainland Southeast Asia and stretched as far north as southern China.
The beginning of the Khmer Empire is conventionally dated to 802, when Khmer prince Jayavarman II declared himself chakravartin (lit. 'universal ruler', a title equivalent to 'emperor') in the Phnom Kulen mountains. Although the end of the Khmer Empire has traditionally been marked with the fall of Angkor to the Siamese Ayutthaya Kingdom in 1431, the reasons for the empire's collapse are still debated amongst scholars. Researchers have determined that a period of strong monsoon rains was followed by a severe drought in the region, which caused damage to the empire's hydraulic infrastructure. Variability between droughts and flooding was also a problem, which may have caused residents to migrate southward and away from the empire's major cities.
