In the aftermath of President-elect Gemayel 's assassination on September 14 , the IDF entered West Beirut , citing a need to prevent civil disorder . While in Beirut Israeli troops allowed the Phalangist-affiliated Lebanese Forces ( LF ) to enter Sabra and Shatila to root out PLO cells believed located there , hundreds of Palestinian refugees were killed in the process . This incident prompted U.S. President Ronald Reagan to organize a new Multinational Force ( MNF ) with France and Italy . On September 29 , this new force entered Beirut , with about 1,200 troops . Their stated mission was to help the new Lebanese government and army with stability . Lebanon 's military predicament began during the last week of June 1982 , when the Maronite-dominated Lebanese Forces ( LF ) militia began to move steadily up the Beirut-Damascus highway toward Alayh , where it engaged militia elements of the Druze Progressive Socialist Party ( PSP ) . The LF , in an effort to establish its presence in new areas , moved into Saida and the western fringes of the Shuf by the end of the month . It was in the Shuf , under the watchful eyes of the IDF , that the LF and PSP maneuvered toward an inevitable confrontation . The significance of the LF advance is that it rekindled the Lebanese civil war . The second deployment consisted of the 2nd Battalion 8th Marine Regiment and U.S. Army Soldiers . They were followed by the 3rd Battalion 8th Marines in October 1982 . The Battalion Landing Team 's headquarters was at Beirut International Airport . France 's contingent of 1,500 paratroopers were based in the coastal part of West Beirut close to the seaport , and the 1,400 Italian troops ( paratroopers of the Folgore Brigade , Bersaglieri regiments and the San Marco Regiment ) were based in the southern part of the city , where refugees are concentrated . In February 1983 , United Kingdom armored cars from 1st The Queen 's Dragoon Guards joined the MNF
killed
Sabra and Shatila massacre
Multinational Force in Lebanon