Israel is attacking Lebanon because of the Hizbollah executed a bold attack on Israel and brazenly taking two soldiers captive prior to the "war". That was the starting point. It has gone downhill from there.
Basically the bottomline, there is a powerplay going on between Iran, Syria, and the Hizbollah to unstablize the region with Israel the target (the plan is to eliminate it) and in the larger scheme of things, aim at the US and its influence. Please note the Lebanon doesn't have any real control over the Hizbollah. They are like a ministate within a state.
The Sunnites which comprise of the majority of the Islamic Arab world aren't too happy with the Hizbollah because they are Shiites which take orders from Syria and Iran (the main Shiite stronghold) in the Islamic world. Essentially, the Shiites and Sunnites are rivals in the Islamic world and the Sunnites have been in control for centuries and the Shiites hope to turn things around by starting trouble. It is very complicated to explain it further than that.
There is potential for this situation get seriously out of control and consume the Middle East. At this point, it will be just plain ugly and eventually calm down again.
