In under four years, Cambodia's government killed about a quarter of its own people. When the communist Khmer Rouge, led by Pol Pot, seized the country in 1975, they declared it "Year Zero." History would start over from scratch. They emptied the cities at gunpoint, marching some two million people out of the capital and forced the entire population onto collective farms. Money was abolished. So were private property, religion, and schools. The goal was a pure agrarian state, built by forced labor. The Communists set out to erase anyone who might think for themselves. Being a doctor, a teacher, or a monk could get you killed. So could speaking a foreign language or simply wearing glasses. To save bullets, executioners often used hammers, hoes and sharpened bamboo. The bodies filled the mass graves that became known as the Killing Fields. By the time a Vietnamese invasion drove the Khmer Rouge out in 1979, between 1.5 and 2 million Cambodians were dead out of a population of roughly 8 million. One in four Cambodians. Dead. Not by war or natural disaster. From their own Communist government.