September 19, 1863. The first day of the Battle of Chickamauga ends in a bloody draw. On the next day, the battle is determined by one of the biggest blunders of the Civil War. Miscommunication, confusion, and fatigue with Union General William Rosecrans and his generals have left a gap in the Union line more than a quarter mile wide. James Longstreet's force of 11,000 from the Confederate Army of Northern Virginia, pour through the gap and split the Union army in two. Rosecrans and his beaten army escape to Chattanooga. Chickamauga's combined casualties of 34,000 are only topped by the carnage at Gettysburg. In October, Rosecrans is replaced by U.S. Grant, who immediately plans an offensive. In November 1863, Grant routes the Confederate stronghold just outside Chattanooga. As they escape southward into Georgia, a Confederate officer calls the devastating defeat: "the death knell of the Confederacy."