There was a refusal to understand - the head of the Joint Chiefs opined that we'd need 400,000+ troops to ensure law and order and a stable country and was fired for giving that opinion to Congress.

And then after the US went in light with just 130,000, Bremer disbanded the Iraqi Army. The insane thing is that he just kind of did it on a whim. The pre-war plan called for the end to Saddam's favored units - the Iraqi Republican Guard - but a significant use of the army in reconstruction efforts and the creation of a new Iraqi government. Bremer and his team looked at that and decided it would be hard, so he decided to just order the army to disband (rather than even try to pull things together and establish order), sent a memo up the chain, and it was approved based on his recommendation in Baghdad. But it was never discussed by the Joint Chiefs, by the National Security Council, or the State Department. Nuts.