Graduating from West Point in 1840, he served as an artillery subaltern in the war against the Seminole Indians[?] in Florida (1841), and in the Mexican War at the battles of Fort Brown, Resaca de la Palma, Monterey and Buena Vista, receiving three promotions for distinguished gallantry in action. From 1851 to 1854 he was an instructor at West Point. In 1855 he was appointed a major of the 2nd Cavalry by Jefferson Davis, then secretary of war.
At the outbreak of the Civil War, three of Thomas' regimental superiors--Albert Sidney Johnston, Robert E. Lee and William Joseph Hardee[?]--resigned. Many southern-born generals were torn between loyalty to their state and loyalty to their country. Thomas struggled with the decision but opted to remain with the United States.
He was promoted in rapid succession to be lieutenant-colonel and colonel in the regular army, and brigadier-general of volunteers. In command of an independent force in eastern Kentucky, on the January 18, 1862, he attacked and routed the Confederate General Zollicoffer at Mill Springs, gaining the first important Union victory in the West.
He served under Don C. Buell[?] and was offered, but refused, the chief command in the anxious days before the battle of Perryville. Under William Rosecrans[?] he was engaged at Stone River and was in charge of the most important part of the manoeuvring from Decherd to Chattanooga. At the Battle of Chickamauga on September 19, 1863, he gained the name of "The Rock of Chickamauga," by some accounts being all that saved a terrible defeat for the North from becoming a hopeless rout.
Thomas succeeded Rosecrans in command of the Army of the Cumberland[?] shortly before the Battle of Chattanooga[?]. In William Tecumseh Sherman's advance through Georgia in the spring of 1864, the Army of the Cumberland numbered over 60,000 men.
When John B. Hood[?] broke away from Atlanta in the autumn of 1864, menaced Sherman's long line of communications and endeavored to force Sherman to follow him, Sherman abandoned his communications and embarked on his infamous march to the sea. Thomas stayed behind to fight Hood. Thomas, with a smaller force, raced with Hood to reach Nashville, where he was to receive reinforcements.
At the Battle of Franklin[?] on November 30, 1864, a large part of Thomas's force, under command of John McAllister Schofield[?], held Hood in check long enough to cover the concentration at Nashville.
At Nashville, Thomas had to organize his force, drawn from all parts of the West and includeding many young troops and even quartermaster's employes. He declined to attack until his army was ready and the ice covering the ground had melted enough for his men to move. The North, including General Ulysses S. Grant himself, grew impatient at the delay. General John A. Logan was sent with an order to supersede Thomas, and soon afterwards Grant left the Army of the Potomac to take command in person.
Before either arrived, Thomas made his attack on December 15, 1864, and the Battle of Nashville[?] was the most crushing defeat of any army on either side in the whole war. Hood's army was completely ruined and never again appeared on the field. For this brilliant victory Thomas was made a major-general in the regular army and received the thanks of Congress.
After the end of the Civil War, Thomas commanded military departments in Kentucky and Tennessee until 1869, when he was ordered to command the division of the Pacific with headquarters at San Francisco. He died there of apoplexy, while writing an answer to an article criticizing his military career, on the 28th of March 1870.
Thomas was beloved by his soldiers, for whom he always had a fatherly concern. His achievements were solid, not brilliant. He never had any ambitions outside of the military, remaining in the army his entire life.
His cadets at West Point gave him the nickname of "Slow Trot Thomas," which characterized him physically and mentally. His mind was deliberate and his temperament sluggish, but he was known for accurate judgment and thorough knowledge of his profession and once he grasped a problem and the time was right for action, he would strike a vigorous, rapid blow.
He was in chief command of only two battles in the Civil War, the Battle of Mill Springs[?] at the beginning and the Battle of Nashville near the end. Both were victories. During the three years between the two battles, he was regarded for loyal obedience to superiors, skillful command of subordinates, and successful accomplishment of every task he was given.