Under Pol Pot 's leadership , the Khmer Rouge regime was responsible for the deaths of millions of ordinary Cambodians during a four-year reign of terror that was eventually halted in 1979 by invading Vietnamese forces . In 1975 , the Khmer Rouge ordered people out of Phnom Penh , the capital , and other cities in Cambodia to work in the countryside . It is said to be responsible for about 1.7 million deaths , roughly a quarter of the population at the time . Its stated aim was to create a Communist utopia , but instead the regime forced Cambodians into what has been described as a living hell . Soldiers marched city-dwellers into the countryside and forced them to work as farm laborers . Those already living in rural Cambodia were expected to produce enough food for the country while teaching farming to those who had never done it before . The regime abolished currency , and considered anyone with an education a threat . It did not allow modern medicine , and it isolated Cambodia to make it completely self-sufficient . The results were disastrous : People died of starvation and disease as soldiers tortured and
-LRB- CNN -RRB- -- Hundreds of Cambodians packed a courtroom in Phnom Penh on Monday as three top Khmer Rouge leaders went on trial for their role during the bloody four-year regime in the mid-1970s . The U.N.-backed Extraordinary Chambers in the Courts of Cambodia has scheduled four days of opening statements for the defendants , who are all in their 80s . On trial are Ieng Sary , the former Khmer Rouge foreign minister ; Khieu Samphon , the nominal head of state ; and Nuon Chea , the prime minister , also known as Brother Number 2 . The head of the Khmer Rouge , Pol Pot , was known as Brother Number 1 . He died in 1998 , long before the U.N.-backed court came into existence . A fourth defendant , Ieng Thirith , was ruled unfit to stand trial because she suffers from dementia and could be set free , prosecutor said . She is Sary 's wife and served as the social affairs ministry during the regime . Prosecutors have charged the defendants with crimes against humanity , grave breaches of the Geneva Conventions , genocide , homicide , torture and religious persecution .