The conflict began in late 1960s and escalated in the 1970s. After the PLO leadership and its Fatah brigade were expelled from Jordan in 1971 for fomenting a revolt, they entered Lebanon and internal and cross-border violence increased. The Palestine Liberation Organization (PLO) had already recruited militants in Lebanon from among the families of Palestinian refugees who were expelled or fled due to the creation of Israel in 1948. By 1968, the PLO and Israel were committing cross border attacks against each other. Meanwhile, demographic tensions over the Lebanese National Pact led to the Lebanese Civil War (1975–1990). PLO was one of the key factors to the eruption of the Lebanese Civil War and its bitter battles with Lebanese factions caused foreign intervention. Israel's 1978 invasion of Lebanon pushed the PLO north of the Litani River, but the PLO continued their campaign against Israel. Israel invaded Lebanon again in 1982, in alliance with major Lebanese Christian militias, and forcibly expelled the PLO. Israel withdrew to a slim borderland buffer zone, held with the aid of proxy militants in the South Lebanon Army (SLA). Israel and Lebanon signed the May 17 Agreement providing a framework for the establishment of normal bilateral relations between the two countries, but relations were disrupted with takeover of Shia and Druze militias in early 1984.