The Khmer Rouge, also known as the Communist Party of Kampuchea, was originally formed in 1951. By the late 1950s, members of the Khmer Rouge engaged in secret coups and efforts to undermine Prince Norodom Sihanouk’s government, although it took many years before the Khmer Rouge made any progress against the Cambodian monarchy since the monarchy already had pre-established connections with other armed forces. After being appointed as the General Secretary of the Communist Party of Kampuchea in 1963, Pol Pot led these attacks on Prince Sihanouk's government.

Throughout the 1960s, the Khmer Rouge pretended to support the Cambodian monarchy in an effort to gain trust of the Cambodian people, especially the residents of the cities. On March 11, 1967, a rebellion broke out between villagers and tax collectors when King Sihanouk was out of the country. The Khmer Rouge used this opportunity to gain more followers after many failed revolts; these actions marked the start of the Cambodian Civil War in 1967. In the years that followed, Lon Nol gained power and took control of Cambodia in 1970. Meanwhile, the Khmer Rouge had gained additional members, becoming a serious threat to the Lon Nol government, as seen by the Khmer Rouge’s early victories over Lon Nol’s forces in battle during 1972. By 1973, 85% of Cambodian territory was controlled by the Khmer Rouge. By this point, the Lon Nol army was growing weaker as they endured continued conflict with the Khmer Rouge. 

Between January and August of 1973, the Khmer Rouge dropped around half a million bombs on different areas of Cambodia. These bombings are estimated to have killed as many as 300,000 people. Lon Nol’s government quickly became unstable as a result of these bombings; Lon Nol officially resigned on April 1, 1975 and fled with his family to Thailand. The Khmer Rouge overtook the capital city of Phnom Penh on April 17th, 1975.