The Khmer empire was a powerful state in South East Asia, formed by people of the same name, lasting from 802 CE to 1431 CE. At its peak, the empire covered much of what today is Cambodia, Thailand, Laos, and southern Vietnam.

By the 7th century CE, Khmer people inhabited territories along the Mekong river -the world's seventh longest river - from the delta to roughly the modern Cambodia-Laos border, plus the region between that river and the great Tonle Sap lake to the west and the area running along the Tonle Sap river (which runs from the lake to the sea, joining the Mekong in the delta). There were several kingdoms at constant war against each other, with art and culture heavily influenced by India due to long established sea trade routes with that subcontinent.

Hinduism mostly, but Buddhism as well, were important religions in the region, mixed with animist and traditional cults. Important cities from that time include Angkor Borei, Sambor Prei Kuk, Banteay Prei Nokor and Wat Phu. A man called Jayavarman II, who is said to have come from a place named Java - which may or may not be the island we call Java in Southeast Asia, led a series of successful military campaigns, subjugating most of these petty kingdoms, that resulted in the founding of a large territorial state. In 802 CE he took the title chakravartin, “universal ruler”, and that date is used to signal the start of the empire. Using the city of Angkor as capital, for the next centuries the Khmer empire expanded its territorial base, mostly to the north (entering the Khorat plateau) and the west, to the Chao Phraya basin and beyond. To the east outcomes were different: several times the Khmer fought wars against two neighboring peoples with powerful kingdoms, the Cham (in today's central Vietnam) and the Vietnamese (in today's northern Vietnam). Despite some victories, as in 1145 CE, when Cham's capital Vijaya was taken, the empire was never able to annex those lands. Conversely, Chams and Vietnamese enjoyed some victories of their own, the most spectacular of which was Cham's humiliating revenge, looting Angkor (1177 CE) and pushing the empire to the edge of destruction.

Throughout the empire's history, Khmer's court was repeatedly concerned with putting down rebellions initiated by ambitious nobles trying to achieve independence, or fighting conspiracies against the king. This was particularly true each time a king died, as successions were usually contested.

The Khmer were great builders, filling the landscape with monumental temples, huge reservoirs (called baray) and canals, and laying an extensive road network with all sorts of bridges -the main highways are 800 km long. The most stunning temple, Angkor Wat, is a microcosm of the Hindu universe and defies imagination as the world's largest religious complex - covering 200 hectares.