Godless secular humanists in the Civil War

I'm about one-third of the way through a fascinating book by Princeton professor of religious history Harry S. Stout. "Upon the Altar of the Nation: A Moral History of the Civil War'' is a door stop of a book, but it is as engaging and well written as any work of history I've read.
Stout points out that one of the many things the Confederacy had against the Union was that it was founded on, quite literally, a godless document. Jefferson and that crowd didn't see fit to put God into the Constitution, something the Confederacy didn't overlook when it made up a constitution. That document invoked "the favor and guidance of Almighty God.''
Fat lot of good it did them.
But they were right that our Constitution did not explicitly call a "Christian'' or even a "Judeo-Christian'' nation into existence. For good reason. You declare yourself such and, ipso facto, anything you do has God's blessing attached to it in black and white. Which is just hooey.
And how happy do you think the Almighty was to have his named dragged into a document that thought slavery was His idea in the first place?