From the Asia Times:
The closing of the Christian womb has ensured eventual Muslim dominance.
Precise data are unobtainable, for demographics is politics in Lebanon, but Lebanon's Christians became as infertile as their European counterparts. Muslims, particularly the impoverished and marginalized Shi'ites, had more babies. In 1971, the Shi'ite fertility rate was 3.8 babies per female, against only 2 for Maronite Christians, or just below replacement. Precise data are not available, but Christian fertility is well below replacement today.
Even before the 1975 Lebanese Civil War, infertility undermined the position of Lebanon's Christians . The civil war itself arose from the demographic shift towards Muslims, who saw the Christian-leaning constitution as unfair. Christianity in the Levant ultimately failed for the same reason that it failed in Europe: populations that are nominally Christian did not trouble to reproduce.