Forces signed the Tripartite Accord in Damascus which is supposed to give strong influence to Damascus regarding Lebanese matters. The agreement never came into effect due to Hobeika's ousting. Two months later Amal militiamen were driven out of West Beirut by their Communist (PLA) and Druze (PSP) rivals in a week of street fighting, artillery exchanges and looting which led to the Syrian army returning to Beirut on 22 February after an absence of three and a half years. On February 17, 1988, the American Chief of the United Nations Truce Supervision Organization (UNTSO) observer group in Lebanon, Lt. Col. William R. Higgins, was abducted and later killed after meeting with Amal's political leader of southern Lebanon. Amal responded by launching a campaign against Hezbollah in the south, It was believed that Hezbollah abducted him; Though the party to this day denies it and insists that it was done to create problems between them and the Amal movement. In April 1988 Amal launched an all-out assault on Hezbollah positions in south Lebanon and the southern suburbs of Beirut. Early in May 1988 Hezbollah gained control of 80% of the Shi'ite suburbs of Beirut through well-timed assaults. In 1989, Amal accepted the Taif agreement (mainly authored by el-Husseini) in order to end the civil war. In September 1991, with background in the Syrian controlled end of the Lebanese Civil War in October 1990, 2,800 Amal troops joined the Lebanese army. Lebanese Civil War War of the Camps The War of the Camps was a series of controversial battles in the mid-1980s between Amal and Palestinian groups. The Druze-oriented Progressive Socialist Party (PSP), the leftists, and also Hezbollah supported the Palestinians, while the Syrian government backed Amal. First battle (May 1985) Although most of the Palestinian guerrillas were expelled during the 1982 Israeli invasion, Palestinian militias began to regain their footing after the Israeli withdrawal from first Beirut, then Sidon and Tyre. Syria viewed this revival with some anxiety: though in the same ideological camp, Damascus had little control over most Palestinians organizations and was afraid that the build-up of Palestinian forces could lead to a new Israeli invasion. In Lebanon, Shia–Palestinian relations had been very tense since the late 1960s. After the multinational force withdrew from Beirut in February 1984, Amal and the PSP took control of west Beirut and Amal built a number of outposts around the camps (in Beirut