Founded in 1957 at Beirut by a group of Lebanese Nasserite activists led by Ibrahim Kulaylat who opposed the pro-Western policies of President Camille Chamoun, the INM came to prominence at the height of the 1958 Civil War.

Consistent with its Pan-Arab ideals, the radical INM was a staunch advocate of the Palestinian cause in Lebanon since the late 1960s, cultivating close political and military ties with the Palestine Liberation Organization (PLO) in the immediate pre-war years.

[5] Quietly re-formed in early 1975, their "Sentinels" militia, now known as the Al-Mourabitoun Forces (Arabic: قوات المرابطون | Quwwat al-Murabitun), started with just 150–200 poorly armed militants,[6] but it subsequently grew to 3,000–5,000 men and women drawn from the Muslim quarters of West Beirut placed under the command of Kulaylat himself.

[7][8] Headquartered at the Tarik al-Jadida quarter of the Corniche El-Mazraa commercial district in West Beirut, the INM/al-Mourabitoun in the early 1980s numbered some 1,000 regular fighters and 2,000 reservists secretly trained by the Palestinian factions (Fatah,[4][9] PFLP and As-Saiqa) and later by Lieutenant Ahmed Al-Khatib's Lebanese Arab Army.

[10] Since its foundation the militia quickly attained a 'regular' outlook, attested by the high discipline and organization of its 3,000 uniformed militiamen into conventional branches of Armor, Infantry and Artillery, backed by Medical, Signals and Military Police support units.

British Bofors 40mm L/60 anti-aircraft guns,[59] Yugoslav Zastava M55 20mm,[49][54][52] Soviet ZPU (ZPU-1, ZPU-2, ZPU-4) 14.5mm[70][52] and ZU-23-2 23mm[60] AA autocannons (mounted on technicals, ZIL-151 trucks and M113 and BTR-152 APCs)[71][72] were employed in both air defense and direct fire supporting roles.

In addition to AA guns and autocannons, the INM/Al-Murabitoun received either from Syria or the PLO a number of man-portable, shoulder-launched Soviet SA-7 Grail surface-to-air (SAM) missiles, which they employed against Israeli Air Force (IAF) fighter-bomber jets during the 1982 Lebanon War.

They also operated two clandestine ports located at Ouza'i district and at the Ain El-Mreisseh waterfront sector of the Lebanese capital, which were used primarily for arms-smuggling in collusion with the Sidon-based Popular Nasserist Organization (PNO).

They also took part on January 20 of that same year in the violent (and controversial) sieges of the Christian towns of Es-Saadiyat, Damour, and Jiyeh in the Iqlim al-Kharrub, on the side of PLO and Palestine Liberation Army (PLA) units to avenge the earlier Tel al-Zaatar massacre by the Lebanese Front militias.

Towards the end of the 1970s heavy casualties and their involvement in atrocities against non-Muslims caused the number of militants from other sects in the ranks to drop sharply, a situation further aggrieved by internal splits that occurred at the early 1980s.

Nevertheless, the al-Mourabitoun did not lost its military capabilities, and during the June 1982 Israeli invasion of Lebanon, they helped the PLO in the defense of the southwestern outskirts of the Lebanese Capital from IDF attacks until the end of the siege in September of that year.

[84] Ibrahim Kulaylat emerged from the wreck of the LNM and the Palestinian withdrawal as the dominant Sunni leader, though he opted not to join the LNRF/Jammoul nor the pro-Syrian LNSF alliances in the mid-1980s, and consequently the political influence of the INM/al-Murabitoun had waned significantly.

[1] Later during the Coastal War in March–April 1985, the Al-Mourabitoun joined in a Syrian-backed coalition with the Popular Nasserist Organization (PNO), the Druze PSP/PLA and the Shi'ite Amal Movement, which defeated the Christian Lebanese Forces (LF) attempts to establish bridgeheads at Damour and Sidon.

When the War of the Camps broke out in April that year at West Beirut, it saw the Al-Mourabitoun allied with the PLO, the Nasserite Sixth of February Movement, the Communist Action Organization in Lebanon (OCAL), and the Kurdish Democratic Party – Lebanon (KDP-L) pitted against a powerful coalition of Shia Amal movement, pro-Syrian SSNP-L,[87] the Lebanese Army,[88] and anti-Arafat dissident Palestinian guerrilla factions of the Palestinian National Salvation Front backed by Syria.