Reminds me of a quote from John Goodman in The Big Lebowski:
"Say what you want about the tenents of National Socialism, Dude, at least it's an ethos."
I tend to believe the Bush administration and the Pentagon knew that an insurgency and civil war were possible, they just didn't want us to think about it, so they avoided talking about it.
They probably thought they would whip a minor Sunni insurgency and the Shi'a would worship us as heroes and the streets of America would flow with pride and oil.
I still believe we lost in Iraq when we failed to crush the Sunni insurgency when it first began to flair up.
Maybe thats too simplistic. I don't know for sure.