1)  The adoption of Indian doctrines of deva-raja or "god-king"

The ancient Khmer kings adopted a successful monarchy system of Indian civilization as the replica. Being revered as the "god-king" or deva-raja, the Khmer kings were able to rule over the empire with divine kingship and absolute power. This enhanced the kings to mobilize large manpower to serve in its military force to defend the nation as well as to invade the neighbors. In addition, the kings could maintain their extensive irrigation system which was the prime factor of its successful economy with their Khmer laborers and foreign slaves. 

Moreover, the kings surrounded themselves with the wise men or the "learned" Khmer Brahmins as their counselors. The Brahmins were known to have acquire vast knowledge which were inherited from father to sons or taught only within the family. These learned Brahmins help the kings to run an efficient administration of the country, and thus resulted in stronger empire.

2)   Strategic Location

Well-chosen strategic location of the Angkor by its founder Jayavarman II hampered the attack by its potential enemies which enable its existence for over 6 centuries.

The Angkor was situated in the North of Tonle Sap Lake, and the only possible way for invaders to bring in a large enough troop to fight against the Angkor is by sailing upstream from the Mekong River. Geographically, the Angkor was protected by rugged thick forests from all sides.  There were no well-developed roads, and the land access with large military force could turn out into a tragedy. The troops and weapons had to be delivered in a long line which could not support one another in case of being attack. A good example is the Persian invasion to the Greeks during the 4th and 5th B.C. Greece for instance was protected by high mountains. Although the Persian was far more superior and much more in number, it could hardly win over the Greeks.

When the enemies intended to attack the Angkor, they have to sail up from the Mekong River only to meet with the strong naval force of Angkor upstream.  The enemy's battle ships moved slower thus became an easier target of being attacked and sunk. Throughout the history of over 600 years, Angkor lose only one major naval battle on Tonle Sap Lake to Champa in 1171.

3)   Mastery over Water Control

The geographical location of the Angkor Empire itself faces two extreme seasons, i.e. the heavy rainfall during Monsoon and the dry period during the off-Monsoon season. Numerous large reservoirs, dikes, moats and ponds helped significantly to prevent floods over the farmland during the heavy rainfall in Monsoon and to conserve water storage for use during the dry season. The efficient and extensive irrigation system of the ancient Khmer enabled the empire to cultivate crops two to three times a year which led to high productivity and strong economy of the Angkor Empire.

1)   Introduction of Theravada Buddhism

The pillar of the Angkor Civilization was supported by the religious belief of Hinduism and Mahayana Buddhism. The monarchs being regarded as the god-king were able to motivate the dedication of their people to serve the throne as a divine service. The empire's extensive irrigation system and military troops required massive laborers and manpower to maintain.   The introduction of Theravada Buddhism in 13th century to the Khmers had turned out to hurt sublimely the basic foundation of the Angkor Empire in the long run. Theravada Buddhism taught the people to seek self-enlightenment, abandon worldly things and discourage any superstition belief which directly or indirectly means all deities and all evils. The sovereignty of the Angkorian monarch as a  "god-king" or deva-raja was basically challenged.

2)  Loss of Water Control

Less devotion of the people to the "god-king" led negative impact to the empire.  The Khmers seem unwilling to work wholeheartedly for the king as a holy service as they had previously did.  The formerly efficient irrigation and drainage system became silted up with less water supply and the rice crops, used to be cultivated two or three times a year, were dramatically dropped, thus weaken the productivity and the strength of the Angkor Empire.

3)  External Threats

As neighboring states of the Angkor grew, they became a major threat to the empire, especially the Thai State of Ayuthaya in the Chaophaya River Basin to the West. In order to protect the empire, the Angkor had to direct portion of its manpower to secure strong armed forces, which in turn, deprived itself from giving good maintenance to its irrigation system.

4)  Double-edged sword of Roads Network

The road network built by Jayavarman VII had aided the transports of products and trades throughout the empire and also facilitated the Khmer troops to quell its neighbors. It had became a double-edged sword when the Angkor became weak as the invaders could easily marched in through this road network, instead of previously sailing up from the Mekong River. This turned out to be true when the newly emerged Ayuthaya, a Thai kingdom in the West became stronger. They use this road to march from the Chaophaya River basin through Phnomrung (in Burirum of modern Thailand) and then through Aranyapathet to attack right at the heart of Angkor and finally sacked the empire in 1431.  The glory of the Angkor Civilization was terminated since that time.

Written by Aphisit W.
Mark Standen: Passage through Angkor