The PLO resettled in Lebanon, where it began to extend a de facto autonomous rule and from which it staged raids into Israel. PLO was one of the major factors for sectarian destabilization of Lebanon and the eruption of the Lebanese Civil War in 1975. In 1978, Israel launched Operation Litani, in which it together with the Free Lebanon Army forced the PLO to retreat north of the Litani river. In 1981 another conflict between Israel and the PLO broke out, which ended with a ceasefire agreement that did not solve the core of the conflict. In June 1982, Israel invaded Lebanon in alliance with Christian factions of the Lebanese government. Within two months the PLO agreed to withdraw thence.