In a vicious spiral of sectarian violence , civilians were an easy target . On 18 January 1976 an estimated 1,000 – 1,500 people were killed by Maronite forces in the Karantina Massacre , followed two days later by a retaliatory strike on Damour by Palestinian militias . These two massacres prompted a mass exodus of Muslims and Christians , as people fearing retribution fled to areas under the control of their own sect . The ethnic and religious layout of the residential areas of the capital encouraged this process , and East and West Beirut were increasingly transformed into what was in effect Christian and Muslim Beirut . Also , the number of Maronite leftists who had allied with the LNM , and Muslim conservatives with the government , dropped sharply , as the war revealed itself as an utterly sectarian conflict . Another effect of the massacres was to bring in Yassir Arafat 's well-armed Fatah and thereby the Palestine Liberation Organisation on the side of the LNM , as Palestinian sentiment was by now completely hostile to the Maronite forces
retaliatory strike on Damour
Damour massacre
Lebanese Civil War