The invasion followed a series of attacks and counter-attacks between the Palestine Liberation Organization (PLO) operating in southern Lebanon and the Israeli military, which had caused civilian casualties on both sides of the border.

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.

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.

No attacks by Palestinian forces on Israel were recorded, while the IDF incursions across the armistice line into Lebanon increased markedly, with minefields being laid, gun posts established, and generally involving numerous violations of Lebanese air-space and territorial waters.

[52] In his report for the period of 12 December 1980 to 12 June 1981 on UNIFIL activities, the Security Council Secretary General noted that infiltrations into the border zone by Palestinian armed forces had decreased relative to the previous six months.

Where the initiator(s) of attacks could be identified in the report, in 15 cases Palestinian militants were to blame while on 23 occasions the Militia and/or the IDF were the instigators, the latter also being responsible for the most violent confrontation of the period on 27 April [paragraph 52].

(The Israeli strikes) led to exchanges of heavy firing between armed elements (Palestinians), on the one hand, and IDF and the de facto forces (Christian Militia) on the other.

Later that same day, UNIFIL observed the firing of rockets from Palestinian positions in the Tyre region into northern Israel, but none of the projectiles hit Israeli towns[62] – the gunners had been ordered to miss.

[63][64] The freedom of movement of UNIFIL personnel and UNTSO observers within the enclave remained restricted due to the actions of Amal and the South Lebanon Army under Major Saad Haddad's leadership with the backing of Israeli military forces.

The President of the U.N. Security Council, Ide Oumarou of Niger, expressed "deep concern at the extent of the loss of life and the scale of the destruction caused by the deplorable events that have been taking place for several days in Lebanon".

[73] In the biography of ceasefire broker Philip Habib, Alexander Haig is cited as leaving the worst impression of all in the lead up to Israel's Lebanon invasion: Haig thus comes off very badly: not a team player, not able to keep the rest of the administration informed of what was going on beforehand, not willing to tell anyone in the White House why Sharon was so confident during the invasion, hoping that Reagan's special envoy would fail in his mission, and having little sense of what the national security of the United States required—which was not a confrontation between Israeli and Soviet tanks on the road from Beirut to Damascus.

Also, according to Shlaim, with the completion of Israeli withdrawals from Sinai in March 1982, under the terms of the Egyptian-Israeli Peace Treaty, the Likud-led government of Israel hardened its attitude to the Arab world and became more aggressive.

[91] On 6 June 1982, Israeli forces under direction of Defense Minister Ariel Sharon launched a three-pronged invasion of southern Lebanon in "Operation Peace for Galilee".

Simultaneously, Israeli armor, paratroopers, and naval commandos set sail in amphibious landing ships from Ashdod towards the Lebanese coast north of Sidon.

One division bypassed Mount Hermon via a road bulldozed by Israeli military engineers and cleared the town of Hasbaiya before swinging right and advancing towards Rachaiya.

[93][36][92] At the same time, an Israeli amphibious operation was conducted north of Sidon, beginning with a diversionary bombardment of targets away from the landing zone by missile boats and aircraft.

Israeli troops began searches for arms caches, and suspected PLO members were systematically rounded up and screened, and taken to a detention camp on the Amoun Heights.

As the fighting raged, an IDF armored unit struck northeast, attempting to bypass Khalde and advance on Baabda, which overlooked the airport and could be used as another staging point to cut the Beirut-Damascus highway.

Syrian units in Beirut and three commando battalions armed with anti-tank weaponry took up defensive positions southwest of the airport to block any Israeli attempt to capture it.

The Israelis advanced relentlessly, and after fourteen hours of fierce combat that raged up through Ain Aanoub and Souq el-Gharb, they broke through the Syrian positions and entered Baabda.

[104] The Soviets were so shaken by the staggering losses sustained by their allies that they dispatched the deputy head of their air defense force to Syria to examine how the Israelis had been so dominant.

Syrian tanks saw similar success against Israeli armor in Ain Zhalta and Sultan Yacoub in fighting on 8–10 June, stemming their advance to capture the Beirut-Damascus highway.

[116] Palestinian Liberation Organization forces continued to grow in Lebanon, with full-time military personnel numbering around 15,000 fedayeen, although only 6,000 of these – including 4,500 regulars – deployed in the south.

[125] The same authors also refer to Israeli intelligence estimates of the number of PLO fighters in southern Lebanon of 6,000 as divided into three concentrations; about 1,500 south of the Litani River in the so-called Iron Triangle (between the villages of Kana, Dir Amas, and Juya), Tyre, and its surrounding refugee camps; another 2,500 of the Kastel Brigade in three districts between the Litani and a line running from Sidon to northeast of Nabatiye; and a third large concentration of about 1,500–2,000 men of the Karameh Brigade in the east, on the slopes of Mount Hermon.

[17] Accurate numbers of total casualties are hard to estimate, due to "[t]he chaos of warfare, the destruction of city neighborhoods and refugee camps, the haste with which bodies were buried in mass graves and the absence of impartial agencies".

[21] In early September 1982, the independent Beirut newspaper An Nahar published an estimate of deaths from hospital and police records covering the period from 6 June to 31 August 1982.

[citation needed] The Mountain War ended after the Christian forces and civilians withdrew to the town of Deir el Kamar, where they were besieged for 3 months before all hostilities ceased and they were transported to East Beirut.

[citation needed] According to Abraham Rabinovich, the complete dominance of U.S. and Israeli technology and tactics over those of the Eastern Bloc was a factor that hastened the demise of the Warsaw Pact and the Soviet Union.

Chairman was Seán MacBride, the other members were Richard Falk, Kader Asmal, Brian Bercusson, Géraud de la Pradelle, and Stefan Wild.

The commission's report[168] concluded that "the government of Israel has committed acts of aggression contrary to international law", that the government of Israel had no valid reasons under international law for its invasion of Lebanon, and that the Israeli authorities or forces were directly or indirectly responsible for the massacres and killings, which have been reported to have been carried out by Lebanese militiamen in Sabra and the Shatila refugee camp in the Beirut area between 16 and 18 September.