Gee, Lebanon didn't seem to have a problem with being occupied by Syria for all those years.
Lebanon didn't exist for all those years as a political entity...it being occupied by Syria. Lebanon only partially exists now, and only on paper in the south...which is what this thing is about.
By "international law" Lebanon is responsible for stopping the attacks across its borders, or is itself responsible for the attacks (clear acts of war). It is clear to everyone that even if "Lebanon" chose to stop Hezballah, it could not even field an army capable of penetrating anywhere near the Isreali border, much less stopping the attacks...thus it is not a sovereign nation. Clearing Hezbollah out of southern Lebanon is a prerequisite for Lebanon becoming a nation.