Great article on why the US march to Baghdad was so effortless, for the most part:

In the final days of the U.S. invasion of Iraq, this country's armed forces collapsed from within, with soldiers deserting in droves and commanders of even the most elite units refusing to push their last fighters toward inevitable slaughter by a technologically superior U.S. force, former Iraqi military leaders said.

The rapid disintegration was largely preordained, Iraqis said. The Iraqi military was composed of disparate and competing armies with no central command authority, top generals inexplicably ordered some units not to fight, and security precautions left officers unable to communicate or to coordinate battle plans, according to interviews with more than two dozen former general officers and other field commanders serving in the regular army and special military units.