It is important to remember that Cambodian history did not begin with the Khmer Rouge. Pol Pot's incredibly harsh regime has garnered the most attention, but the Cambodians have enjoyed a long and often triumphant history.
Anybody who witnesses the magnificent temples at Angkor can attest to the fact that the Khmer Empire was once wealthy, militarized, and a major force in the region. Its zenith came under Jayavarman VII (1181-ca. 1218), where the Empire made significant territorial gains from the Cham. The Khmer Empire stretched to encompass parts of modern day Thailand, Malaysia, Burma, Laos and Vietnam.
The period following the fall of the Khmer Empire has been described as Cambodia's dark ages. Climatic factors precipitated this fall, where the Ankorian civilization harnessed Cambodia's water for agriculture through elaborate systems of canals and dams. The Khmer Empire never recovered from the sacking by its neighbors based in Ayutthaya (in modern day Thailand), and Cambodia spent much of the next 400 years (until French colonization) squeezed and threatened by the rivalries of the expanding Siamese and Vietnamese Empires to the West and East. Indeed, on the eve of French colonization it was claimed that Cambodia was likely set to cease to exist as an independent kingdom entirely, with the historian John Tully claiming “there can be little doubt that their [the French] intervention prevented the political disappearance of the kingdom”.
The French came to dominate Cambodia as a protectorate from the 1860s, part of a wider ambition to control the area then termed Indochina (modern day Cambodia, Vietnam and Laos). The French were always more concerned with their possessions in Vietnam. Education of Cambodians was neglected for all but the established elite. It was from this elite that many "Red Khmers" would emerge. Japan's hold on Southeast Asia during the Second World War undermined French prestige and, following the Allied victory, Prince Sihanouk soon declared independence. This was a relatively peaceful transition as France was too absorbed with its struggle in Vietnam, which it saw as more important to its conception of L'Indochine francaise.
Prince Sihanouk was the main power figure in the country after this. He was noted for making very strange movies in which he starred, wrote and directed. His rule was characterized at this point with a Buddhist revival and an emphasis on education. This, however, was a mixed blessing. He succeeded in helping create an educated elite who became increasingly disenchanted with the lack of jobs available. As the economic situation in Cambodia deteriorated, many of these young people were attracted to the Indochinese Communist Party, and later the Khmer Rouge.
As the Second Indochina War spread to Cambodia's border (an important part of the "Ho Chi Minh trail"), the USA became increasingly concerned with events in the country. The US Air Force bombed Cambodia from 1964 to 1973. During this campaign, which was initially codenamed Operation Menu, 540,000 tonnes of bombs were dropped. Estimates of the death toll range from 40,000 to 150,000. Most of the bombing was done in support of Khmer Republic military forces fighting the Khmer Rouge and North Vietnam. In total, the US dropped 2.7 million tonnes of bombs on Cambodia from 1964 to 1973, more than the combined amount dropped by all the Allies in all theatres during World War II.
In March 1970, while overseas to visit Moscow and Beijing, Sihanouk was overthrown by Lon Nol and other generals who were looked upon favorably by the United States. Sihanouk then put his support behind the Khmer Rouge. This change influenced many to follow suit; he was, after all, considered a Boddhisatva. Meanwhile the Khmer Rouge followed the Vietnamese example and began to engender themselves to the rural poor. Between 200,000 and 300,000 people died in the civil war including the United States air campaigns.
Following a five-year struggle, Communist Khmer Rouge forces captured Phnom Penh in 1975 and ordered the evacuation of all cities and towns. Over one million people (and possibly many more) died from execution or enforced hardships. Those from the cities were known as "new" people and suffered the most at first. The rural peasantry were regarded as "base" people and fared better. However, the Khmer Rouge's cruelty was enacted on both groups. It also depended much upon where you were from. For example, people in the East generally got it worse. It is debated whether or not the Khmer Rouge began "crimes against humanity" or a protracted "genocide". There are claims that there were a disproportionate number of ethnic Chams killed, and the ethnically Vietnamese also suffered persecution.
Nonetheless, the Khmer also suffered often indiscriminate mass killings. A 1978 Vietnamese invasion drove the Khmer Rouge into the countryside and ended 13 years of fighting (but the fighting would continue for some time in border areas). As a result of the devastating politics of the Khmer Rouge regime, virtually no infrastructure was left. Institutions of higher education, finance, and all forms of commerce were destroyed in 1978, so the country had to be rebuilt from scratch. UN-sponsored elections in 1993 helped restore some semblance of normalcy, as did the rapid diminution of the Khmer Rouge in the mid-1990s. A coalition government, formed under pressure of the losing party following national elections in 1998, brought renewed political stability and the surrender of remaining Khmer Rouge forces. Many leaders of the formal periods kept important positions. They often adopted more liberal views as long they could extract personal profit of the situation.
SOURCE: http://wikitravel.org/en/Cambodia