Geographical and climatic setting:
Being a part of Southeast Asia, Cambodia is located by the Gulf of Thailand, sandwiched between Vietnam to the east and Thailand to the west and north, and shares a border with Laos in the northeast. Conveniently situated right on the busy trade routes of both land and sea, the people who occupied Cambodia since ancient times experienced triumphs and defeats as well as glory and decay, all due to the dynamic nature of the region's peoples and their economic/historical development.
Geography and climates influenced people and their way of making a living, thus empires may not rise and fall without first getting their economic system in order.
Location is important, but geographical and climatic features dictate how people lived and developed.
Cambodia's most visible element is the Mekong River and the vast areas that are flooded annually, and the great lake called Tonle Sap, home to the largest source of fresh-water fish in the world.
To approach its geography mentally, one can get oriented to its location on the gulf next to Thailand, or start from the source of the Mekong in the Himalayas. Follow the river and see it wind over 2000 miles southward through China, Burma, Thailand, Laos, Cambodia and Vietnam, its exit point into the South China Sea.
Just before the Mekong River flows into the border region of Cambodia and Vietnam, it is joined by the Tonle Sap River. A geographical phenomenon happens at this confluence every year. During the dry season, the Tonle Sap River drains the water southward from the great lake and joins the Mekong to the sea. At the peak of the wet season, when the monsoon rain adds to the spring melt from the Himalayas, the volume of Mekong water reaches flood stage and in full force.
So powerful is the river's desire to burst that it forces the flow of the Tonle Sap river to change its course, and part of the Mekong water now flows northward and increases the volume of the great lake by three times, which is already so big during the dry season; at the center of the lake, one cannot see anything but water all around, much like being in the middle of a brown ocean. Since ancient times, this lake supported a large population with an endless supply of fish and fresh water.
As the rain inundates the entire South and Southeast Asian landscape from around April to November, the rivers there overflow to flood the farm land and riverside forests, the promise of life is apparent. The rich coat of silt and bountiful supply of water are two key elements in the livelihood of the people in region.
The monsoon is responsible for life, and sometimes death. The seasonal wind that brings moisture northward from the ocean will cease and dry wind from central Asian desserts will bring dry weather from around November to April. This cycle of weather pattern set the rhythm of life throughout the region. Up to three rice crops can be yielded annually from many places.1
As the rain promises life, the flooded landscape and raging rivers make travelling a near-impossible task. In the case of Southeast Asia, add to that the numerous mountain chains and any efforts to make contacts with the outside world by land are that much more of a challenge, even in the dry season.
This is Southeast Asia: the people so geographically isolated and developed differently from one another, yet linked by the monsoon climatic system, and the dynamic cycles of water. The Khmer kingdom at its peak in the 9th to 12th century occupied a large chunk of southern mainland and peninsular Southeast Asia: all of today's Cambodia, southern Vietnam (Cochin China), southern and northeast Thailand (Issan), southern Laos, and half of peninsular Malaysia.2
Ideally situated at the crossroad of trades, Khmer people had land access to Siam, Burma, and India, as well as Annam, Champa, and China; whereas its coastline stretched from today's southern Vietnam all the way to cover almost the entire length of the Gulf of Thailand, offered access to and from just about anywhere by sea, from India to China, and places in between. Spread out over five million square hectares, the Khmer landscape is flat and unbroken, covered with rich mineral deposits, had numerous and precious natural resources of plants and animals.
However, not having any major mountain chains to deter invaders, the lay of the land offered easy access from the west by the invading Siamese and Burmese, while a small mountain chain to the east hardly kept out the Vietnamese and the Cham.3
Water is abundant and annually renew the soil through flood, offered great agricultural potential for population growth. As mentioned, today's southern Vietnam was part of the Khmer political entity, thus the Mekong delta with its enormous agricultural and fishing potentials no doubt contributed to the growth and strength of the Khmer Kingdom.
Back to the interior, the Tonle Sap Lake offered an almost inexhaustible source of fish and fresh water. As wet rice cultivating is the main agricultural activity, catching fish to supplement their diet is the Khmer's answer to easy work. As the great lake recedes and flows back into the Mekong river in the dry season, the locals can easily trap large amounts of fish that had fattened in the lake-- which submerged large tracts of forest in the monsoon months-- in the relatively narrow channel of the Tonle sap river.4
This is the essence when thinking about the huge monuments that were built: there had to be a large and efficient population with sufficient food supply that can support such extravagance. To puts things in perspective, the Khmer and their neighbors owe much of their existence and history to the nature of the land and the seasonal wind that brings the rain.