The secondary name is derived from General Robert E. Lee's Special Order 191, which detailed the C.S. Army of Northern Virginia's invasion of the Union through the border state Maryland in September 1862. Turtledove creates a divergence at September 10, 1862, when three Union soldiers do not find a copy of Special Order 191, as they in fact did historically. Historians believe their find helped General George B. McClellan of the Army of the Potomac prepare for his confrontation with Lee, and contributed to the Union's eventual victory at the Battle of Antietam.