[7] At the outbreak of the Lebanese Civil War, the country was home to a large Palestinian population divided along political lines.

[8] Many of the inhabitants left to fight with As-Sa'iqa between January and June 1976, and this led to the Arab Liberation Front, another PLO faction, gradually assuming de facto control of the camp.

[8][better source needed] On April 13, 1975, a group of Phalangist[9] militiamen led an ambush on a bus that was on its way to the Tel al-Zaatar camp, killing twenty-seven and injuring nineteen.

[10] Following the killing of five Phalangists in the Christian controlled area of Fanar on December 6, 1975, Maronite local militia captured hundreds of Muslims in East Beirut at random.

[14] The Christian forces were initially leery of escalating PLO involvement in the war, but Karantina was inhabited partly by Lebanese Muslims and was located along the main road they needed to resupply their positions in Beirut, so it was considered a legitimate target.

[17] To complicate matters further, there were unaffiliated fighters present who fought under the PLO umbrella but did not support any one faction, mostly foreign fedayeen.

[18][better source needed] The siege began in January 1976 when a van full of essential items such as food and medical supplies was stopped from entering the camp.

[21] From June 22 onward, the Tigers militia led by Danny Chamoun, and many Christian residents of Ras el-Dekweneh and Mansouriye controlled by Maroun Khoury, intensified the blockade to a full-scale military assault that lasted 35 days.

[18] Repeated attempts by outside Palestinian factions to assist those inside the camp was met with ill fortune due to complications with the competing groups.

[21] The raising of Palestinian and Lebanese flags in the area was a sign of provocation that led to an increased military assault in late July.

"[24][25] When Arafat visited the survivors, who had been relocated to Damour after Palestinian militias had massacred the civilian population there, he was reportedly shouted down as a "traitor" and pelted with rotten vegetables.

[24][26] The siege enabled Bachir Gemayal to strengthen his position as the head of the Unified Military Command of the Lebanese Front militias.