from the war lived in Phnom Penh and other cities. On New Year's Day 1975, Communist troops launched an offensive which, in 117 days of the hardest fighting of the war, led to the collapse of the Khmer Republic. Simultaneous attacks around the perimeter of Phnom Penh pinned down Republican forces, while other CPK units overran fire bases controlling the vital lower Mekong resupply route. A US-funded airlift of ammunition and rice ended when Congress refused additional aid for Cambodia. The Lon Nol government in Phnom Penh surrendered on 17 April 1975, just five days after the US mission evacuated Cambodia. Khmer Rouge regime, 1975–1978 The Khmer Rouge reached Phnom Penh and took power in 1975. Led by Pol Pot, they changed the official name of the country to Democratic Kampuchea. The new regime modelled itself on Maoist China during the Great Leap Forward, immediately evacuated the cities, and sent the entire population on forced marches to rural work projects. They attempted to rebuild the country's agriculture on the model of the 11th century, discarded Western medicine, and destroyed temples, libraries, and anything considered Western. Estimates as to how many people were killed by the Khmer Rouge regime range from approximately one to three million; the most commonly cited figure is two million (about a quarter of the population). This era gave rise to the term Killing Fields, and the prison Tuol Sleng became notorious for its history of mass killing. Hundreds of thousands fled across the border into neighbouring Thailand. The regime disproportionately targeted ethnic minority groups. The Cham Muslims suffered serious purges with as much as half of their population exterminated. Pol Pot was determined to keep his power and disenfranchise any enemies or potential threats, and thus increased his violent and aggressive actions against his people. Forced repatriation in 1970 and deaths during the Khmer Rouge era reduced the Vietnamese population in Cambodia from between 250,000 and 300,000 in 1969 to a reported 56,000 in 1984. However, most of the victims of the Khmer Rouge regime were not ethnic minorities but ethnic Khmer. Professionals, such as doctors, lawyers and teachers, were also targeted. According to Robert D. Kaplan, "eyeglasses were as deadly as the yellow star" as they were seen as a sign of intellectualism. Religious institutions were targeted by the Khmer Rouge particularly fiercely. Religion was so viciously persecuted to such a terrifying extent that the