In 1975, after years of civil war, Cambodia suffered a devastating blow to its development as the Khmer Rouge took control of Phnom Penh. Khmer Rouge leader Pol Pot's vision for a Cambodia absent of any social institutions such as banks, universities, religions or any modern technology centered on a return to an agrarian communist society.
The means of implementation were to exterminate anyone who didn't fit within this new ideal. The "new" nation was being turned back to "Year Zero", and intellectuals, businessmen, doctors, Buddhist leaders and foreigners were "purged." It is estimated that 1.5 to 2 million people--25% of the population--were killed during this time.
The Khmer Rouge did not stop killing Cambodians until 1998, when Pol Pot died.