From the Hoover's Larry Diamond,
"...Iraq today falls far short of what the Bush administration promised. As a result of a long chain of U.S. miscalculations, the coalition occupation has left Iraq in far worse shape than it need have and has diminished the long-term prospects of democracy there. Iraqis, Americans, and other foreigners continue to be killed. What went wrong? ...
In truth, around 300,000 troops might have been enough to make Iraq largely secure after the war. But doing so would also have required different kinds of troops, with different rules of engagement. The coalition should have deployed vastly more military police and other troops trained for urban patrols, crowd control, civil reconstruction, and peace maintenance and enforcement. Tens of thousands of soldiers with sophisticated monitoring equipment should have been posted along the borders with Syria and Iran to intercept the flows of foreign terrorists, Iranian intelligence agents, money, and weapons.
But Washington failed to take such steps, for the same reasons it decided to occupy Iraq with a relatively light force: hubris and ideology. Contemptuous of the State Department's regional experts who were seen as too "soft" to remake Iraq, a small group of Pentagon officials ignored the elaborate postwar planning the State Department had overseen through its "Future of Iraq" project, which had anticipated many of the problems that emerged after the invasion. Instead of preparing for the worst, Pentagon planners assumed that Iraqis would joyously welcome U.S. and international troops as liberators..."
...Yadda-yadda-yadda. Wussamatter, Larry -- didn't you get that memo?