The 1982 Lebanon War, also called the Second Israeli invasion of Lebanon, began on 6 June 1982, when Israel invaded southern Lebanon. The invasion followed a series of attacks and counter-attacks between the Palestine Liberation Organization (PLO) operating in southern Lebanon and the Israel Defense Forces (IDF), which had caused civilian casualties on both sides of the border. The Israeli military operation, codenamed Operation Peace for Galilee, was launched after gunmen from the Abu Nidal Organization attempted to assassinate Shlomo Argov, Israel's ambassador to the United Kingdom. Israeli prime minister Menachem Begin blamed the PLO, using the incident as a casus belli. It was the second invasion of Lebanon by Israel, following the 1978 South Lebanon conflict. The Israelis sought to end Palestinian attacks from Lebanon, destroy the Palestine Liberation Organization (PLO) in the country, and install a pro-Israel Maronite Christian government. Israeli forces attacked and overran PLO positions in southern Lebanon and briefly clashed with the Syrian Army, who occupied most of the country's northeast. The Israeli military, together with the South Lebanon Army, seized control of the southern half of Lebanon and laid siege to the capital Beirut. The Lebanese Forces however, despite their clandestine alliance with Israel, refused to participate in the war against the PLO as their leader Bachir Gemayel viewed any direct involvement as assisting an invading army. Surrounded in West Beirut and subjected to heavy Israeli bombardment, the PLO and their allies negotiated a ceasefire with the aid of United States special envoy Philip Habib. The PLO, led by Yasser Arafat, were evacuated from Lebanon, overseen by a multinational peacekeeping force. By expelling the PLO, removing Syrian influence over Lebanon, and installing a pro-Israeli Christian government led by President Bachir Gemayel, the Israeli government hoped to sign a treaty that would give Israel "forty years of peace". Following the assassination of Gemayel in September 1982, Israel's position in Beirut became untenable and the signing of a peace treaty became increasingly unlikely. There was outrage at the IDF's role in the Israeli-backed, Phalangist-perpetrated Sabra and Shatila massacre of Palestinians and Lebanese Shias. This stoked Israeli public disillusionment with the war. The IDF withdrew from Beirut and ended its operation on 29 September 1982. The May 17 Agreement of 1983 ended the state of war between Israel and Lebanon, and provided for an Israeli withdrawal from the country. Amid rising casualties from guerrilla attacks, the IDF retreated south of the Awali river on 3 September 1983. From February to April 1985, the Israeli military undertook a phased withdrawal to its "South Lebanon security zone" along the border. The Israeli occupation saw the emergence of Hezbollah, an Iranian-backed Shia Islamist group. It waged a guerrilla war against the Israeli occupation until the IDF's final withdrawal from Lebanon in 2000. In Israel, the 1982 invasion is also known as the First Lebanon War.