The LYM was founded in the early 1970s as an association of Maronite right-wing university students, who strongly opposed the 1969 Cairo Agreement and the presence of Palestine Liberation Organization (PLO) guerrilla factions in Lebanon, by Maroun el-Khoury (nom de guerre "Bash Maroun"), the son of the former head of the Dekwaneh district of East Beirut, Naim el-Khoury.

Personally commanded by Bash Maroun, they usually operated in the Ras-el-Dekwaneh, Ain El Remmaneh and Mansouriye districts, manning the local sections of the Green Line, but also fought in other areas (namely at the Battle of the Hotels), earning a reputation of fierce combatants.

In January–August 1976, a force of 100 LYM/MKG militiamen took part in the sieges and subsequent massacres of the Palestinian refugee situated at the coastal town of Dbayeh in the Matn District, and at Karantina, Al-Maslakh and Tel al-Zaatar in East Beirut.

At the latter battle, the LYM/MKG intensified the blockade of the refugee camp by launching on 22 June a full-scale military assault that lasted for 35 days,[1][2] and the cruelty displayed by LYM/MKG members' in this assault and other atrocities, earned them the unflattering nickname "The Ghosts of the Cemeteries" (Arabic: أشباح المقابر | 'Ashbah al-Maqabir) – Bash Maroun's men were normally seen wearing necklaces made from human body parts cut from their victims.

Under LF command, they later again played a key role in the eviction of the Syrian Army out from the Christian-controlled East Beirut in February 1978 during the Hundred Days' War.