The Khmer Rouge was a communist revolutionary government in Cambodia in the mid/late 70’s. It was founded by a group of largely western-educated Cambodians who entirely rejected concepts of the free market and individual liberties.
Instead, they attempted to construct an entirely self-sustaining nation through a rigid regime of top-down social engineering.
This included the abolishment of banking, finance, currency, and some religions. People living in urban areas were (often forcibly) moved to the rural areas of the country to work in agriculture (again, often against their will).
It was a bold and frankly inhuman stab at what could conceivably be called a “classless” society. In all, an estimated 1 to 3 million people (out of a population of slightly over 8 million) perished as a result of the policies of his four-year premiership
The genocide came in a number of forms, which included but were not limited to:
Famine. The urban workers relocated to the fields knew nothing about agriculture, so land was not nearly cultivated to its full potential, resulting in mass famine almost immediately after the regime took control.
Disease. The Khmer Rouge believed that the country should be autonomous in all respects, including medicine. If the country did not have the resources to produce a certain drug, that drug was entirely unavailable (at least to the non-ruling class). As a result, thousands died to common and preventable diseases.
Execution and reeducation. Violations of the regime’s anti-capitalist tenets were generally punishable by death. If you hoarded food, you could be executed. If you harvested wild crops, you could be executed. If you traded for a profit, you could be executed. Naturally, if you ever spoke out (publicly or privately) against the regime or its principles, you could be executed. Needless to say, corporal punishment was doled out without judicial process. Additionally, torture and execution were doled out on those suspected of being an enemy of the regime. This included anyone with material ties to the former government, many people with college-level educations, individuals of other ethnic backgrounds (including Chinese, Vietnamese, Thai), virtually any practicing religious person, anyone unable to grow their assigned crops (at quotas well in excess of those achievable before the regime took power), almost anyone who spoke English or French, and even people who simply wore glasses.
In short, it was an attempt to reboot civilization (sans capitalism) and establish a society without wealth or class. As explained above, the Khmer Rouge did not tolerate non-believers well.
The last interview with Pol Pot (leader of Khmer Rouge)