After the end of hostilities between Syria and Israel on 31 May 1974, guerrilla forces of the Palestinian Liberation Organization (PLO) continued to launch a series of raids into Israel from camps in Lebanon. In 1975, fighting broke out between Lebanese Christians and Palestinians. Very quickly, Lebanese Muslims entered the fray on the side of the Palestinians. The situation quickly developed into a full-scale civil war with the Christians pitted against the Muslims/Druse and the Palestinians. The Palestinians, however, were not uniformly Muslim. Indeed, the conflict did not neatly divide along sectarian lines. This fact was clearly demonstrated during an offensive in late December 1975 when the Lebanese Christian forces overran two small Palestinian camps and executed all males over the age of about 12. Palestinian Christians populated both camps! The PLO supported the Lebanese Muslims and used southern Lebanon as a base for artillery and rocket attacks on northern Israeli settlements.
The PLO attacks on Israeli settlements continued unabated. On 14 March 1978, Israeli forces invaded southern Lebanon with the objective of eliminating PLO bases. On 19 March 1978, the United Nations (UN) Security Council passed a resolution calling for the withdrawal of Israeli forces and their replacement by a peacekeeping force, the UN Interim Force in Lebanon (UNIFIL). By mid-April, UN troops had replaced Israeli units in Lebanon. The UNIFIL initially included 117 Canadian troops, but Canada withdrew from this mission once it was launched.