I'm thinking WWIII has already begun. Hostilities will continue to escalate until it becomes painfully obvious. Years later, historians will try to pinpoint when WWIII began, and settle on a specific occurrence like the Cole bombing, 911, or the invasion of Afghanistan. Only time will tell.
The precipitating event was the return of Khomeini to Iran. Much like Germany dropping Lenin back into Russia during WWI started the Cold War. We will see an ugly, vicious war.
Iran, Lebanon, Somalia and the current spasm by the left over Iraq have shown our enemies that we are weak.
The barbarian hordes are on the march and there are too many in the US and Europe who say we need to understand them rather than kill them.