The Palestine Liberation Organization (PLO) recruited militants in Lebanon from among the Palestinian refugees who had been expelled or fled after the creation of Israel in 1948. After the PLO leadership and its Fatah brigade were expelled from Jordan in 1970–71 for fomenting a revolt, they entered Southern Lebanon, resulting in an increase of internal and cross-border violence. 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 Lebanese Forces and Kataeb Party, and forcibly expelled the PLO. In 1983, 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. Israel withdrew from most of Lebanon in 1985, but kept control of a security buffer zone, held with the aid of proxy militants in the South Lebanon Army (SLA).