Civilizations expand through trade, conflict, and exploration. Usually, all three elements must be present for a civilization to grow and remain stable for a long period of time. Trade
The Khmer maintained vibrant trading relationships throughout East Asia, the Indian subcontinent, and even Europe and Africa through the Silk Road, a collection of both overland and maritime trade routes. The primary conflicts of the Khmer civilization were waged with neighboring communities—the Cham, the Vietnamese, and the Thai. The Cham were a collection of kingdoms in what is today central and southern Vietnam, while the ancient Vietnamese influence extended through what is today northern Vietnam. Thai kingdoms such as Sukothai and Ayutthaya flourished in what are now Thailand, Cambodia, and Malaysia. The Khmer civilization relied heavily on rice farming, and developed a complex irrigation system to take advantage of the rivers and wetlands that dotted their territory. An efficient series of irrigation canals and reservoirs, called barays, allowed fewer farmers to produce more rice. This, in turn, allowed more people to pursue non-agricultural lifestyles and migrate to great urban areas, such as Angkor.
