The Khmer Empire was in Southeast Asia.
Cambodia ( [ kæmˈboʊdiə ] កម ព ជ , or Kampuchea [ kɑmpuˈciə ] ) , officially known as the Kingdom of Cambodia ( ព រ រ ជ ណ ចក រកម ព ជ , Preăh Réachéanachâk Kâmpŭchéa , [ ˈprĕəh riəciənaːˈcɑk kɑmpuˈciə ] ) , is a country located in the southern portion of the Indochina Peninsula in Southeast Asia . Jayavarman II ( c. 770 -- 835 ) was a 9th-century king of Cambodia , widely recognized as the founder of the Khmer Empire , the dominant civilisation on the Southeast Asian mainland until the mid 15th century . Khmer Empire . The empire , which grew out of the former kingdoms of Funan and Chenla , at times ruled over and/or vassalised most of mainland Southeast Asia . In this year , King Jayavarman II had himself declared chakravartin ( `` king of the world '' , or `` king of kings '' ) on Phnom Kulen .