The Confederates had already pushed the night before, and on the morning of September 20, they practically swarmed across Chickamauga Creek. The Northern men were stunned by the violence of the attack, and they fell back.

General Longstreet, meanwhile, was asked only to make a demonstration on his section, but he probed and found a gap nearly a quarter of a mile long in the federal center. This was because of Rosecrans’ rebuking an officer the night before, then sending an order for him to march to his left. That officer knew it might create havoc, but he decided to carry out the order to the letter rather than risk another verbal slap. Longstreet could hardly believe his good luck. Though he received no approval from Bragg, Longstreet went ahead, marching his 12,000 men in a tightly packed formation right into the gap, just to the left of the Union center. This was the kind of opportunity field officers dreamed of: an opening that would split the enemy’s force in two.