Leaving most of central Beirut in shambles and perhaps permanently dividing Beirut in half, the the civil war that took place in Beirut from 1975 to 1990 is probably the most influential events in the history of the city. The civil war was the result of a complicated series of events, however, this page will attempt to provide a concise summary of the factors, causes, and results of the war.

After World War I, Beirut was made the capital of Lebanon by the French Mandate. The Muslims of Beirut, however, opposed the inclusion of the city in a "Christian-dominated Lebanon" and "declared loyalty to a broader Pan-Arabism" than most of the Christian residents would agree to. Tensions increased between the Christians and Muslims as Beirut grew in both economic importance and in population.

In 1948, thousands of Palestine refugees fled from the Arab-Israeli War and settled in Beirut. The influx of Palestine immigrants fueled the conflict between the Christians and Muslims in Beirut. In 1970, the Palestine Liberation Organization (PLO) set up its military and administrative headquarters in West Beirut after being exiled from Jordan. The PLO, an organization made up of Arabs that lived in Palestine before Israel was created, was formed in 1964 to unite the various Palestinian groups in hopes of creating a "democratic and secular" Palestinian state. In Beirut, the PLO launched several raids into Israel. The Christian-dominated government of Lebanon responded by attempting to stop any further military action by the PLO. In turn, the PLO offered its sympathy to the Muslims of Beirut.

The conflict between the Muslims and Christians in Beirut culminated in a destructive civil war. Open warfare between the Christians and the Palestinians and Muslims began in about 1975. The city became visibly separated as the Muslims and Palestinians conducted retreated to West Beirut and the Christians to East Beirut. As the violence between the two sides intensified, Syria, fearing Israeli invasion, sent in 20,000 troops to "prevent destruction of the Christian community." United Nations forces were also sent in hopes of maintaining a cease-fire between the two groups. In June of 1982, Lebanon was invaded by Israeli forces in hopes of driving out the Palestinian forces. The Israeli Army surrounded West Beirut and after a series of "full-scale attacks" and negotiations the PLO was evacuated from West Beirut. The Christian militia of Lebanese Forces and the the Lebanese Army maintained order in East Beirut, however, religious factions and different Muslim militias in West Beirut "repeatedly clashed with one another in what resembled total anarchy." In 1989, West Beirut was subjected to months of shelling from the Lebanese Army of East Beirut. Just as the end of the conflict became realistic, a strange twist of events prevented peace in Beirut. The Lebanese Army and the Christian Militia of Lebanese Forces of East Beirut, in a dispute about a peace accord, fought each other in East Beirut and ended up destroying much of the Christian community. Peace in Beirut was finally established in 1990, however, Isreali forces occupied southern Lebanon for many years later.