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Civil War and occupation

With the 1970 defeat of the PLO in Jordan, many Palestinian militants relocated to Lebanon, increasing their armed campaign against Israel. The relocation of Palestinian bases also led to increasing sectarian tensions between Palestinians versus the Maronites and other Lebanese factions.

In 1975, following increasing sectarian tensions, largely boosted by Palestinian militant relocation into South Lebanon, a full-scale civil war broke out in Lebanon. The Lebanese Civil War pitted a coalition of Christian groups against the joint forces of the PLO, left-wing Druze and Muslim militias. In June 1976, Lebanese President Élias Sarkis asked for the Syrian Army to intervene on the side of the Christians and help restore peace. In October 1976 the Arab League agreed to establish a predominantly Syrian Arab Deterrent Force, which was charged with restoring calm. PLO attacks from Lebanon into Israel in 1977 and 1978 escalated tensions between the countries. On 11 March 1978, 11 Fatah fighters landed on a beach in northern Israel and hijacked two buses full of passengers on the Haifa – Tel-Aviv road, shooting at passing vehicles in what became known as the Coastal Road massacre. They killed 37 and wounded 76 Israelis before being killed in a firefight with Israeli forces. Israel invaded Lebanon four days later in Operation Litani. The Israeli Army occupied most of the area south of the Litani River. The UN Security Council passed Resolution 425 calling for immediate Israeli withdrawal and creating the United Nations Interim Force in Lebanon (UNIFIL), charged with attempting to establish peace.

Israeli forces withdrew later in 1978, but retained control of the southern region by managing a 19-kilometre-wide (12 mi) security zone along the border. These positions were held by the South Lebanon Army (SLA), a Christian militia under the leadership of Major Saad Haddad backed by Israel. The Israeli Prime Minister, Likud 's Menachem Begin, compared the plight of the Christian minority in southern Lebanon (then about 5% of the population in SLA territory) to that of European Jews during World War II. The PLO routinely attacked Israel during the period of the cease-fire, with over 270 documented attacks. People in Galilee regularly had to leave their homes during these shellings. Documents captured in PLO headquarters after the invasion showed they had come from Lebanon. Arafat refused to condemn these attacks on the grounds that the cease-fire was only relevant to Lebanon.

In April 1980 the presence of UNIFIL soldiers in the buffer zone led to the At Tiri incident. On 17 July 1981, Israeli aircraft bombed multi-story apartment buildings in Beirut that contained offices of PLO associated groups. The Lebanese delegate to the United Nations Security Council claimed that 300 civilians had been killed and 800 wounded. The bombing led to worldwide condemnation, and a temporary embargo on the export of U.S. aircraft to Israel. In August 1981, defense minister Ariel Sharon began to draw up plans to attack PLO military infrastructure in West Beirut, where PLO headquarters and command bunkers were located.

In 1982, PLO attacks from Lebanon on Israel led to an Israeli invasion, aiming to support Lebanese forces in driving out the PLO. A multinational force of American, French and Italian contingents (joined in 1983 by a British contingent) were deployed in Beirut after the Israeli siege of the city, to supervise the evacuation of the PLO. The civil war re-emerged in September 1982 after the assassination of Lebanese President Bachir Gemayel, an Israeli ally, and subsequent fighting. During this time a number of sectarian massacres occurred, such as in Sabra and Shatila, and in several refugee camps. The multinational force was withdrawn in the spring of 1984, following a devastating bombing attack during the previous year.

During the early 1980s, Hezbollah, a Shiite Islamist militant group and political party, came into existence through the efforts of Shiite clerics who were financially supported and trained by Iran. Arising in the aftermath of the 1982 war and drawing inspiration from the Islamic Revolution in Iran, Hezbollah actively engaged in combat against Israel as well as suicide attacks, car bombings and assassinations. Their objectives encompassed eliminating Israel, fighting for the Shia cause in the Lebanese civil war, ending Western presence in Lebanon, and establishing a Shiite Khomeinist Islamic state.

In the late 1980s, as Amine Gemayel ’s second term as president drew to an end, the Lebanese pound collapsed. At the end of 1987 US$1 was worth £L500. This meant the legal minimum wage was worth just $17 a month. Most goods in shops were priced in dollars. A Save the Children director estimated that 200,000–300,000 children were need of assistance and were living almost entirely on bread, which was subsidized by the government. Those who could relied on foreign assistance. Hezbollah was receiving about $3–5 million a month from Iran. In September 1988, the Parliament failed to elect a successor to President Gemayel as a result of differences between the Christians, Muslims, and Syrians. The Arab League Summit of May 1989 led to the formation of a Saudi–Moroccan–Algerian committee to solve the crisis. On 16 September 1989 the committee issued a peace plan which was accepted by all. A ceasefire was established, the ports and airports were re-opened and refugees began to return.

In the same month, the Lebanese Parliament agreed to the Taif Agreement, which included an outline timetable for Syrian withdrawal from Lebanon and a formula for the de-confessionalization of the Lebanese political system. The civil war ended at the end of 1990 after 16 years; it had caused massive loss of human life and property and devastated the country's economy. It is estimated that 150,000 people were killed and another 200,000 wounded. Nearly a million civilians were displaced by the war, and some never returned. Parts of Lebanon were left in ruins. The Taif Agreement has still not been implemented in full and Lebanon's political system continues to be divided along sectarian lines. Conflict between Israel and Lebanese militants continued, leading to a series of violent events and clashes including the Qana massacre. In May 2000, Israeli forces fully withdrew from Lebanon. Since then, 25 May is regarded by the Lebanese as the Liberation Day. The internal political situation in Lebanon significantly changed in the early 2000s. After the Israeli withdrawal from southern Lebanon and the death of former president Hafez al-Assad in 2000, the Syrian military presence faced criticism and resistance from the Lebanese population.

On 14 February 2005, former Prime Minister Rafic Hariri was assassinated in a car bomb explosion. Leaders of the March 14 Alliance accused Syria of the attack, while Syria and the March 8 Alliance claimed that Israel was behind the assassination. The Hariri assassination marked the beginning of a series of assassinations that resulted in the death of many prominent Lebanese figures. The assassination triggered the Cedar Revolution, a series of demonstrations which demanded the withdrawal of Syrian troops from Lebanon and the establishment of an international commission to investigate the assassination. Under pressure from the West, Syria began withdrawing, and by 26 April 2005 all Syrian soldiers had returned to Syria.

UNSC Resolution 1595 called for an investigation into the assassination. The United Nations International Independent Investigation Commission published preliminary findings on 20 October 2005 in the Mehlis report, which cited indications that the assassination was organized by Syrian and Lebanese intelligence services.