As Noam Chomsky has said, Washington was expecting the Iraq war to be a quick and easy win. The superior American military power should have easily overwhelmed a sanction-weakened Iraq. Saddam Hussein was indeed not loved by most of his people, and if his overthrow had been handled more carefully, there may have been significant support for the Americans. But the incredibly clumsy, arrogant and savage behaviour of the military (which for many reasons isn't the fault of individual troops who are doing their best to do their job) created increasing hatred towards the U.S.
Steadily losing control of the Iraqi population, the only tactic left for this brutal occupation is divide and conquer. The divide part has succeeded pretty well; the conquer part, not so much.
Of course, even if it were handled well, the occupation of Iraq would not have been justified. However, fewer people would have died, and that's no small thing.
