In March 1978, 20,000 Israeli forces invaded and occupied south Lebanon and established a "security zone" following repeated incursions into Israel from southern Lebanon by the Palestinian National Liberation Movement, the PLO's guerrilla movement.

Under pressure from the UN Security Council, Israel withdrew from the territory, but transferred control of a border strip to the pro-Israeli Christian militias in Lebanon. The UN Security Council adopted Resolution 425, which called for the withdrawal of Israeli troops from south Lebanon and established a UN Interim Force in Lebanon (Unifil), to maintain peace across the border.

Israeli invasion

The security zone is three to six miles wide

Despite the 1978 attack, and the deployment of Unifil, Palestinian guerrilla forces succeeded in re-establishing a military presence in southern Lebanon. Border clashes increased. On June 6 1982 Israeli troops invaded Lebanon, in an attempt to remove the PLO military threat to Israel's northern border.

Israeli troops rapidly advanced, occupying the west of Beirut and trapping 6,000 Palestinians in the southwest of the country. US diplomatic effort eventually secured the dispersal of Palestinian fighters to other Arab countries.

In September 1982, the Phalangist Christian militia attacked Palestinian refugee camps at Sabra and Chatila in retaliation for the assassination of the Christian President-elect of Lebanon. Many of the inhabitants were massacred while Israeli forces stood by.

A peace agreement between Israel and Lebanon, signed in May 1983 called for an end to all hostilities and the withdrawal of all foreign troops from the country. It also provided for security arrangements for Israel in south Lebanon.

Israeli forces are used to combat Hezbollah

However, neighbouring Syria, which exercises significant control over Lebanon, refused to remove its troops from the country, prompting Israel to declare that its forces would not leave Lebanon until Syria's did.

Israel redeployed its troops to the three to six mile wide "security zone" along the border in Southern Lebanon and has remained in control of the area ever since. Israel also armed the pro-Israeli Christian militia, the South Lebanon Army (SLA), to help it police the region.

Continuing attacks

The Israeli campaign failed to remove the PLO threat to its northern towns. Attacks by Palestinian guerrillas on Israel, and fighting between the Iranian backed Hezbollah forces and the pro-Israeli militias continued throughout the mid-1980s, until a cease-fire was agreed between the militias in September 1989.

UN resolution 425 calls for the withdrawal of Israeli troops

The relationship between Lebanon and Syria grew significantly closer from May 1991, when the two countries signed a bilateral treaty. This established formal structures for the creation of links in political, military and economic affairs. In September 1991 Syria and Lebanon signed a mutual security agreement.

In June 1991, Israel launched attacks on Palestinian bases in southern Lebanon, ostensibly in response to attacks by the Hezbollah guerrilla groups. Fighting escalated again in the autumn of 1992.