the prestige the siege was giving PLO leader Yasser Arafat, got all sides to agree to a cease-fire and terms for the PLO's withdrawal on 12 August. The Multinational Force in Lebanon arrived to keep the peace and ensure PLO withdrawal. The PLO leadership retreated from Beirut on 30 August 1982 and moved to Tunisia. The National Assembly of Lebanon narrowly chose Bachir Gemayel as president-elect, but when he was assassinated on 14 September 1982, Israel reoccupied West Beirut. In parallel, Maronite militia Kataeb Party carried out the Sabra and Shatila massacre. 1983 Israeli-Lebanese accords and their collapse In 1983, the United States brokered the May 17 Agreement, a peace treaty between Israel and Lebanon in all but name. The agreement called for a staged Israeli withdrawal over the next eight to twelve weeks and the establishment of a "security zone" to be patrolled by the Lebanese army in southern Lebanon, but was conditional on Syrian withdrawal as well. In August 1983, as Israel withdrew from the areas southeast of Beirut to the Awali River, Lebanese factions clashed for control of the freed territory. In February 1984, the Lebanese Army collapsed, with many units forming their own militias. Shia and Druze militias took over much of Beirut in early 1984 and consolidated power. The National Assembly of Lebanon, under pressure from Syria and Muslim militias, cancelled the 17 May Agreement on 5 March 1984. On 15 January 1985, Israel adopted a phased withdrawal plan, finally retreating to the Litani River to form the deep Israeli Security Zone (map at) while using the native South Lebanese Army militia to help control it. SLA conflict with Hezbollah (February 1985 – May 2000) Consolidation of Hezbollah On 16 February 1985, Shia Sheik Ibrahim al-Amin declared a manifesto in Lebanon, announcing a resistance movement called Hezbollah, whose goals included combating the Israeli occupation. During the South Lebanon conflict (1985–2000) the Hezbollah militia waged a guerrilla campaign against Israeli forces occupying Southern Lebanon and their South Lebanon Army proxies. "Throughout the period of 1985–92, there were very few limited exchanges between Israeli and Hezbollah or Amal forces in southern Lebanon", and "with the exception of 1988, during which twenty-one Israeli soldiers were killed, the number of Israeli fatalities per year over this period was in the single-digit figure". By the end of 1990 the Lebanese Civil War was effectively over. In March 1991, the National