Because of the energetic defiance of Major-General George Thomas. A Virginian by birth and a slaveholder at one time, Thomas was distrusted by the Union top command, and this may have slowed his promotion. At Chickamauga, however, he displayed the terrific fighting capacity that his men knew existed. Bringing his brigades into a semicircle of their own, Rosecrans held Snodgrass Hill and Horseshoe Ridge against repeated Confederate assaults: some of these were led by former Vice President John C. Breckinridge. Only toward evening did Thomas give up the fight and lead his men in an orderly withdrawal. By then, there was not the slightest doubt the Confederates had won: the only question concerned the magnitude of their victory.