Even before the establishment of the Palestine Liberation Organization (PLO) in 1964, exiled Palestinian intellectuals residing in Lebanon and other Arab countries began to form clandestine paramilitary groups in the late 1950s, which later evolved into the main PLO guerrilla factions. In Lebanon, some of these groups would later raise roadblocks where Lebanese people were forced to pay "tolls" to support the Palestinian cause. This alienated important sectors of the native population, in particular the Christian Maronite and Shia communities. Beginning in the late 1960s, Palestinian factions also gradually turned the Jabal Amel region of Southern Lebanon into a "de facto" state of their own, using it as a base for launching guerrilla attacks on Israel. Although in time the Shia community would support the Palestinians in their struggle against Israel, the PLO's and the more radical Rejectionist Front groups' behavior in Southern Lebanon made many Lebanese Shias resent the Palestinian presence. The Palestinians put the Shias of the Jabal Amel at risk by attacking the Israelis from Lebanon, which in turn invited harsh retribution from the Israel Defense Forces (IDF). In 1978, the IDF invaded Southern Lebanon (Operation Litani) in response to the guerrilla attacks made by the PLO from South Lebanon.