Hilzoy marks the Iraq anniversary:
The first Gulf War had a purely military objective: kick the Iraqi army out of Kuwait. This was popular with Kuwaitis, for obvious reasons. More to the point, however, Kuwait had not been occupied for long. There was an existing social and political structure that just needed to be put back in place. So we had no complicated political tasks to achieve within Kuwait itself. Everything we needed to do could be done with military force, and we have the best military force in the world.
Invading Iraq was, obviously, completely different. Iraqis needed to set up a society virtually from scratch. They badly needed our help: help like ensuring basic law and order after the regime fell, and protecting infrastructure from looting. Even if we had not failed utterly to do those things, though, their task would have been immensely difficult.
Imagine how much is presupposed by the fact that I can walk down a street in Baltimore and assume that no one will rob me, or bundle me into a car and hold me for ransom; or by the fact that people who own warehouses or equipment yards need to protect their property against small groups of people, but not against trained private armies. There are, after all, a lot of people who need money, and yet, oddly enough, very few of them do these things. A whole lot goes into making that true: culture, policing, a whole network of shared understandings and assumptions and social mores. In a country like Iraq, when you excise a tyrannical government, all of that is gone.