Lebanon

The main cause of the Lebanese Civil War was that the fragile balance between the Maronite Christians, Sunni Arabs, and Shiite Arabs was in a precarious position and the arrival of the PLO (Palestinian Liberation Organization) in Lebanon threatened to tip the scales. As a result, each faction took to battle in order to increase their stake in the country's leadership. This conflict eventually spilled over into Israel and Syria, leading to those countries ending the War.

The causes of the Lebanese Civil War included, but were not limited to:

1. The rising percentage of Shiite Muslims and sinking percentage of Maronite Christians and the Shiites wanting more power.
2. The arrival of Palestinian Militant Organizations like the PLO fleeing Jordan after King Hussein's Black September who brought unrest and chaos with them.
3. The languishing, horrible conditions of the vast numbers of Palestinian Refugees in Lebanon.
4. The increasing militancy and radicalization of the Maronite Christian minority.
5. The increasing Syrian support of Shiite Paramilitary Groups

Israel entered the Lebanese Civil War on account of the following two reasons:

1. Palestinian Paramilitary Organizations began to rain rockets down on Northern Israel in an attempt to goad Israel to enter the Lebanese Civil War. The PLO believed that such an entry would unite the Shiites and Sunnis behind one banner to repel the Israelis. The Union did not form, but Israel did retaliate by crossing the border and hunting down the PLO.
2. Christian Falangists, with whom Israel quickly allied, promised Israel a longer term ceasefire and more amicable relations in the future. Israel wanted a chance at peace with Lebanon and therefore supported those who would advocate for this.