How did rice agriculture lead to prosperity and power for the Khmer Empire?

officially the Angkor Empire the predecessor state to modern Cambodia ("Kampuchea" or "Srok Khmer" to the Khmer people), was a Hindu-Buddhist empire in Southeast Asia. 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 and parts of Southern China, stretching from the tip of the Indochinese Peninsula northward to modern Yunnan province, China, and from Vietnam westward to Myanmar.