My reference goes more to the point that from the time we first invaded Iraq we fought with the protection of innocents as a high priority.
Sherman was one of the first to demonstrate the theory that when civilian populations pay a price for war, they quickly decide that war is not what they want.
My point is that if the war was fought with those methods from the day we decided to attack Iraq, there would have never been an insurgency.
I'm a Sherman fan, but I think you're misreading this in a big way. Sherman took his campaign to the plantations in order to take the war to those who had imposed it on poor Southerners. I could elaborate on this, but suffice it to say that there are a number of reasons that Sherman's goals were far different from the goals we had in 2003, and applying his methods would have been pointless.
Certainly the air-heavy campaign we used would not have produced the result you're thinking if we had just increased it. Pick up a copy of "The Bomber War" by Robin Neillands and take a look at what he has to say about the population of Germany and their will to fight. Bombing and other destruction did nothing to damage their will, but only focused an unreasonable hatred on the bomber crews. Neillands records one oral account about a crewman who had bailed out over germany and was attacked by a mob of civilians that included nuns.
The key element that led to insurgency was the disbanding of the Iraqi army.