Martin van Creveld, one of the most respected contemporary military historians, has called the invasion of Iraq "the most foolish war since Emperor Augustus in 9 BC sent his legions into Germany and lost them." For those who aren't military scholars, he was referring to a Roman expedition into Germany which was ambushed by 'barbarians' and essentially wiped out. Fighting continued for a few years afterwards, but the barbarians beat off the Roman 'superpower' and this was the end of Roman expansion east across Europe... a few centuries later, those barbarians were in charge of Rome.
In the next couple of years something similar will happen to America as its troops are withdrawn from Iraq, the 'World's Last Superpower' defeated by 'barbarians' with AK-47s, RPGs and cell phones. This is inevitable for a very simple reason; the occupation of Iraq is a vanity war for Americans, but a matter of life and death for Iraqis. America gains nothing from the continual occupation, Americans are already tired of it and Bush will be lucky to hold off the withdrawal until after the next election so he can blame his successor.
There was never any serious American interest in Iraq, which is precisely why the US government had to lie to justify the invasion. There were no nuclear weapons ready to be used at short notice, and there was no al Qaeda presence worth noting. Sure, Saddam Hussein was a thug, but only a thug could hold Iraq together, and he was no worse than many leaders America supports (just as it previously supported him). Yes, maybe he provided some money to terrorist groups, but most of the radical Islamic groups in the UK appear to be funded by Saudi Arabia, supposedly our ally.
When the Americans do pull out, with thousands of American troops dead and hundreds of thousands of Iraqis, what will anyone have gained? The only real winners will be the American corporations who suck at the Pentagon's tax-funded teats, the Shi'ite leaders, who are largely backed by Iran, which is supposed to be our enemy, and the radical Islamic insurgents who will gain a huge amount of prestige by defeating a Superpower. Encouraged by that success, what will stop them from taking their battle to other nations in the region, which we currently rely on for oil?
Some have claimed that the war was fought to steal Iraq's oil, but we'd have saved a lot of money by just buying it. Others have claimed it was fought for Israel, but van Creveld is an Israeli and he's called for Bush to be impeached for invading Iraq. Others that it was intended to 'shock and awe' America's enemies into surrender, but it's merely proven that America's incredibly expensive military is a paper tiger that can't even defeat a third-rate opponent. Others believe that Bush deliberately wants to start WWIII in the Middle East to fulfil Biblical prophecies and bring about Armageddon.
Unfortunately, the reality is probably far worse; Bush is a cheerleader with nukes. Just as Rome in decline was run by lunatics and fourth-rate leaders who could never have managed to build up such an Empire, so is modern America. As the country goes into deep decline, Iraq will be the furthest that the American Empire spreads into the Middle East before the Empire itself falls apart.
Military historians of the future will probably have even less flattering opinions of the invasion of Iraq than van Creveld.