I posted this before:
Clearly the Cambodian and Indochina people went through an awful period. Pol Pot did extreme things as a leader but the alternative of leaving Lon Nol in power who had people starving was not good either. Whether communism or Islamic fundamentalism, anti-colonialism wars are not fun to live through. Here is a perspective I picked up from the Internet.

"A Finnish inquiry commission concludes that 1 million or fewer people died in the Pol Pot period. The commission documented that at least several thousand of those were because of direct military battles with Vietnam. Part of the discrepancy in death figures comes from those who fail to account for the decrease in births that inevitably happens when a population is lacking adequate food and fighting a war. These missed births get counted as deaths in population projections that assume the birth rate did not change."

"The United States war in Southeast Asia killed 600,000 people in Cambodia according to the Finnish Inquiry Commission. The total U.S.-caused deaths in Indochina run into the millions."

"By 1975, an estimated 10 percent of the Kampuchean population -- 600,000 -- had already died as a result of the Vietnam War. Those 600,000 deaths were caused by U.S. efforts to track down Vietnamese communists. According to the Peter Jennings documentary "The Killing Fields", Cambodia specifically absorbed 500,000 tons of U.S. bombs in the early 1970s."

"The U.S.-instigated war -- and the bombings in particular -- also caused the creation of 2 million refugees, who flooded the cities. The cities then came to depend on the U.S. food aid to live because of the war and the inefficiency of the right-wing Lon Nol regime."

"Hence, Pol Pot and the Khmer Rouge seized power from Lon Nol in 1975 in the worst possible situation: The people were starving, Kampuchea was the poorest country in the world and one-third of its people were refugees."

"Executions and other deaths"

"The Boston Globe coverage of Pol Pot's death contained this characterization of the Khmer Rouge: "When the Khmer Rouge marched into the capital on April 17, 1975 to establish their agrarian society, they chased out city dwellers at gunpoint, killed anyone suspected of being an intellectual, forced millions into labor camps, and demanded that children inform on their parents. People were often arrested simply for wearing glasses or knowing a foreign language. Money and private property were abolished, schools and temples were shuttered, and medicine and food became scarce. During a nearly four-year reign, as many as 2 million people died of starvation, execution illness or overwork."

"Pol Pot did execute between 75,000 and 150,000 people between 1975 and 1979. Most of those executions took place in the context of war between Vietnam and Cambodia.Vietnam invaded in 1978 and threw the Khmer Rouge out of power.The famous skull-pile pictures from Kampuchea come from a policy especially aimed at the Vietnamese.Serious famine followed again after the final Vietnamese invasion of December 1978, and by the time international aid started it was too late for many. A total of 2 million, or 30 percent of the population, died in the 1970s from the U.S. war, the Pol Pot period and Vietnamese invasions."

"The United States aided the Khmer Rouge in the 1980s, because they were enemies of U.S. foes, the Vietnamese, who had invaded and ousted the Khmer Rouge in 1979."