George Henry Thomas (1816-70), American military leader, born in Southampton County, Virginia, and educated at the U.S. Military Academy. He served in the Mexican War from 1846 to 1848 and taught at West Point from 1851 to 1854. In 1855 he became a major and was stationed in Texas, where he remained until 1860. At the outbreak of the American Civil War in 1861, Thomas chose to remain loyal to the Union. Commissioned a brigadier general in 1862, he defeated Confederate troops at Mills Springs and took part in the battles of Shiloh and Stones River. At Chickamauga in September 1863, Thomas resisted the concentrated attack of a triumphant enemy, becoming known as the Rock of Chickamauga. He succeeded General William Starke Rosecrans as commander of the Army of the Cumberland, and in November he figured prominently in the Battle of Chattanooga. His men made up half the Union force responsible for the fall of Atlanta in 1864. Thomas's resounding victory in the Battle of Nashville in December 1864 won him the thanks of Congress and a promotion to major general in the regular army. From 1865 to 1869 he held commands in Tennessee and Kentucky, and in June 1869 he was given command of the Military Division of the Pacific.