The Isreali army is powerful. Only their politicians are morons.
If the US Army was doing their job - we'd be running back here with our tails between our legs, or having 5,000 soldiers die a year. We suck at street-level guerilla warfare. We're a bomb and blow kinda army.
Hizbollah has about two thousand full time gunmen, and over 10,000 part-timers. Many more armed Shia will turn out if, say, Israel were to invade south Lebanon again. The Lebanese army has about 70,000 troops. Plus, there are 14,000 internal security troops and police.