The 1967 Muslim-Jewish war and the Palestinian increased involvement in Lebanon

The 1967 Arab-Israel war further strained the relationship between Christians and Muslims. This was due to the fact that the Lebanese political leadership refused to commit its troops to the June 1967 Arab-Israeli war. The non-commitment enraged many Lebanese Muslims[12]. After the defeat of the Arabs in the 1967 war, the Palestinians started to launch attacks against Israel from Lebanon. Israel retaliated by shelling Lebanese towns and villages.

Aziz Abu-Hamad showed that the Palestinian military action against Israel divided Christians and Muslims again:

Muslim leaders proclaimed support for the Palestinian cause, Christian leaders expressed their opposition to dragging Lebanon into the Middle East conflict[13].

Although Lebanese Muslims had only minority representation in the Lebanese Parliament, they outnumbered Christians in 1968. This was largely due to the higher rates of Christian emigration and higher Muslim birth rates. Aziz Abu-Hamad explained that in 1968, Muslims demanded several government changes including an end to the accord that reserved key positions for Maronites, such as the Commander of the army and the Governor of the central Bank[14].

The Cairo agreement of 1969 gave Palestinians the right of autonomous administrative control over their refugee camps in Lebanon. Christians objected to the agreement arguing that it was a betrayal of Lebanese sovereignty[15]. The Christians' anger compelled Christian parties such as Phalanges(Kata'ib) and Camille Chamoun's National Liberal parties to establish military camps for their militias[16]. These newly trained Christian militias assisted the Lebanese army in their clashes with Palestinians in 1970. Although that crisis was temporarily resolved by reaffirming the Cairo Agreement, the Christian leadership, girded for the next round, determined to uphold Lebanese sovereignty and the Christian character of Lebanon[17].

The Jordanian army expelled Palestinian fighters in September 1970 from Jordan. The move was aimed to stop the Palestinians from attacking Israel who used to militarily retaliate by bombing Jordan[18]. Many newly arrived expelled Palestinian fighters entered Lebanon taking advantage of the 1969 Cairo agreement, which granted Palestinian relative autonomy in Lebanon. Aziz Abu-Hamad said that several Lebanese factions, mostly Muslim and leftist groups, used the PLO's autonomy and political and military power to press for greater participation in decision-making[19].

During the 1973 Arab-Israeli war, differences between Christians and Muslims deepened. The Christians were upset to see South Lebanon a battlefield between Israel and the Palestinians, while the Muslims took the opportunity in return to show dissatisfaction with their economic and political status in a Christian dominated political system[20].