I would cite Uchronia even if they didn't quote me at the start of Introduction: What is Alternate History? But if they seem a little too scholarly, try Wikipedia's entries on Alternative history (fiction) and its cousin, the secret history.
Captain Confederacy's piece of the alternate history genre is a very popular one. The first alternative Civil War story was written before the war began: Edmund Ruffin's Anticipations of the Future, published in 1860, is a story about an independent South that was written by a Southerner who feared what would happen if Lincoln was elected.
Edmund Ruffin Fires First Shot of Civil War summarizes it this way:
In Ruffin's novel the Republicans elect William H. Seward as President in 1860. In power, the Republicans proceed to "negroize" society, Ruffin's term for granting social equality to blacks. The white daughters of prominent abolitionists in Washington vie with each other to win the favor of the black ambassador from Haiti, the "Count of Marmalade." When the North emancipates the slaves, the South secedes from the Union, and Owen Brown, son of John Brown, leads an army of blacks southward against the seceders. Much to the surprise of the Northerners, however, the members of the black army desert, return to the plantations where they were raised and, on bended knees, beg their former masters to please reenslave them. With their black army depleted by desertions, the North has no choice but to surrender to the South.Yes, there are a lot of stupid speculations in the field of alternative history. But there are some great ones, too. When Captain Confederacy was being published, I ran this:
A Short Reading List of Southern Alternative History
Bisson, Terry. Fire on the Mountain. Arbor House, 1988. A slave revolt creates a black nation in the American South. The parts of the story set in the 19th century are wonderful.
Churchill, Winston S. “If Lee Had Not Won the Battle of Gettysburg.” Essay, 1931. (Available in If It Had Happened Otherwise, J. C. Squire, ed., St. Martin’s, 1972.) One of the earliest bits of Confederate alterniana.
Kantor, MacKinlay. If the South Had Won the Civil War. Bantam Books, 1961. (Also available in Story Teller, a collection of Kantor’s essays.) Charmingly naive, says yr. humble correspondent.
Moore, Ward. Bring the Jubilee, 1955. Perhaps the finest novel in this tiny sub-genre.
Poyer, David C. The Shiloh Project. Avon Books, 1981. An entertaining espionage tale.
Williams, Walter Jon. “No Spot of Ground.” Novella in What Might Have Been, Vol 2, Benford and Greenberg, eds. Bantam Books, 1989. Edgar Allan Poe lives to become a Confederate officer. It’s grand.