Khmer Rouge
From 1975 to 1978, Pol Pot, also known as Saloth Sar, took control of Cambodia, turning it into a paradise for all, atleast, that's what he thought. In reality around a quarter of the population got killed because of his rule. That number could be as high as 2 million. After the country's regime was left unstable due to internal struggles, he took power in 1975, turning the country communist like most of it's neighbouring countries.
Red Terror
Pol Pot believed that the perfect society was one that solely relied on the countryside. Creating an agrarian socialist society he ordered his country to all abandon the cities and everything modern. His Year Zero idea was to destroy about everything and start all over again. Everyone with glasses, braces, gold teeth, prosthetics and about every minority would be purged. Pol Pot said because they weren't pure. His true motives were probably because he was a bit insane and paraniod, he simply did not trust anyone. The Khmer Rouge soldiers were constantly picking new citizens to first torture to choose a new target and then kill. It could also be a fellow soldier or even a superior officer.