Lebanon was NOT a soley Christian nation since its inception. It started as a mustaffarite to protect the Christians, yes, but then after WW1 it was a mandate of the LON and the Maronites who came to negotiate FOR the size of Lebanon wanted a greater Lebanon DESPITE the fact that it would have INCLUDED a sizeable plurality of non-Christians, which do includes Druze who are neither Muslim OR Christians.
Then Lebanon became independent as a multi-confessional republic. But then, between 1947-1948, the Mandate of Palestine erupted into inter-ethnic fighting for who would have controlled it, and those who lost got expelled in all possible directions, with this changing further and permanently the religious demographic make-up of Lebanon. Then Black September happened, and those lost again, got expelled, and relocated mainly to Lebanon.
It was SO Christian that Bachir Gemayel went to war with Lebanese Christian Armenians to have the control of all Christian neighbourhoods. It was so Christian that it was an ally of Israel, one of the main reasons why Christianity is 43 per cent of Lebanon populations.