michael, you'd have a war with about 20 fronts if you had the whole region break out, with about 20 different parties fighting different fights.
Believe me, no state in the Middle East really gives a rip about the fate of the Palestinians. They're a pawn used for political purposes. As for Lebanon, the US probably has Israel on a bit of a leash there. If things escalate, the US can yank it a bit.
This is also a way to keep Syria busy and take some heat off the US in Iraq. It will all backfire in the end. It will probably cause some Christians to re-think their future in Lebanon.