It was the incessant attempts by Israel to invade Lebanon and the inaction of the Lebanese government but I guess your answer responds to your underlying allegiances.
Israel invaded Lebanon for the same reason every time - to prevent attacks on civilians from Lebanese territory.
https://en.wikipedia.org/wiki/Palestinian_insurgency_in_Sout...
Israel invaded Lebanon for the same reason every time - to prevent attacks on civilians from Lebanese territory.
https://en.wikipedia.org/wiki/Palestinian_insurgency_in_Sout...