The first volume covers the battle of Gettysburg, though with strategic maneuvers beyond anything contemplated by the actual participants. Like any successful counterfactual history, the authors are careful in their initial changes - in fact, most readers will not even be aware of the changes in the battle to after the end of the first day's fighting, but by this point many small changes have already occurred - enough changes in fact to lead Lee to a strategic masterstroke on a par with Jackson's Chancellorsville march.  From here the story rapidly diverges from what we know as history, but never beyond possibility, and it's amusing to see various participants like Sykes, Sickles, Joshua Chamberlain and others perform in this parallel universe.

The battles scenes are excellent and provide a closeup look at the experience of individual troops.  They note often how the opposing sides would arrange unofficial truces when the battles end. You'll probably suspect that the climactic battle of the second book won't resolve everything since there's still that third volume!  But that never subtracts from the tension & suspense of these books. Great history -  my only regret is that Gingrich didn't start writing novels earlier, rather than spending so much time fighting other battles in Congress.

One small annoyance is the tendency of the authors to put anachronistic quotes in the mouths of their actors.  The most prominent one was during a race between the armies towards the coast in which a general remarks "let the man on the farthest edge of the flanking troops touch the sea with his sleeve" - a statement actually made 50 years later in World War I by a German general during their flanking attack through Belgium.  There are several more of these pillaged pedantries scattered thru the books, but their effect, fortunately,  is minimal.