Between 1985 and 1989, sectarian conflict worsened as various efforts at national reconciliation failed. Heavy fighting took place in the War of the Camps of 1985-86 as a Syrian-backed coalition headed by the Amal militia sought to rout the PLO from their Lebanese strongholds. Many Palestinians died, and the Sabra, Shatila, and Bourj al-Barajneh refugee camps were largely destroyed. (Fisk, 609)
Major combat returned to Beirut in 1987, when Palestinians, leftists, and Druze fighters allied against Amal, eventually drawing further Syrian intervention. Violent confrontation flared up again in Beirut in 1988 between Amal and Hezbollah. Hezbollah swiftly seized command of several Amal-held parts of the city, and for the first time emerged as a strong force in the capital.
Muslim groups rejected the violation of the National Pact and pledged support to Selim al-Hoss, a Sunni who had succeeded Karami. Lebanon was thus divided between a Christian military government in East Beirut and a civilian government in West Beirut.
Mouawad was assassinated 16 days later in a car bombing in Beirut on 22 November as his motorcade returned from Lebanese independence day ceremonies. He was succeeded by Elias Hrawi (who remained in office until 1998). Aoun again refused to accept the election, and dissolved Parliament.
On January 31, 1990, Lebanese Army forces clashed with the LF, after Aoun had stated that it was in the national interest for the government to "unify the weapons" (i.e. that the LF must submit to his authority as acting head of state). This brought fierce fighting to East Beirut, and although the LF made initial advances, the intra-Christian warfare eventually sapped the militia of most of its fighting strength.
In August 1990, the Lebanese Parliament, which didn't heed Aoun's order to dissolve, and the new president agreed on constitutional amendments embodying some of the political reforms envisioned at Taif. The National Assembly expanded to 128 seats and was for the first time divided equally between Christians and Muslims.
As Saddam Hussein focused his attention on Kuwait, Iraqi supplies to Aoun dwindled.
On October 13, Syria launched a major operation involving its army, air force (for the first time since Zahle's siege in 1981) and Lebanese allies (mainly the Lebanese Army led by General Émile Lahoud) against Aoun's stronghold around the presidential palace, where hundreds of Aoun supporters were executed . It then cleared out the last Aounist pockets, cementing its hold on the capital. Aoun fled to the French Embassy in Beirut, and later into exile in Paris. He was not able to return until May 2005.
William Harris claims that the Syrian operation could not take place until Syria had reached an agreement with the United States, that in exchange for support against the Iraqi regime of Saddam Hussein in the Gulf War, it would convince Israel not to attack Syrian aircraft approaching Beirut. Aoun claimed in 1990 that the United States "has sold Lebanon to Syria" (Harris, p. 260).