When the South Won
What would North America be like if the South had won the Civil War? Author Harry Turtledove examines the idea in his book How Few Remain. The book is the first in the Timeline-191 series. The story's alternate history begins on September 10, 1862.
History tells us that on September 10, 1862, a Confederate messenger lost General Robert E. Lee's Special Order 191. The order outlined General Lee's plans for the Invasion of the North. Union soldiers found General Lee's orders. The orders were used by George McClellan to defeat the Army of Northern Virginia at the Battle of Antietam.
In How Few Remain, General Lee's orders are recovered by a Confederate soldier. As a result McClellan is caught by surprise. General Lee forces McClellan into battle on the banks of the Susquehanna River in Pennsylvania, resulting in the destruction of the Army of the Potomac in the Battle of Camp Hill on October 1.