in Pennsylvania. He was assigned to Ft. Atkinson, Iowa Territory, from 1842 until 1845. He was the fort's commander during most of that period. He was promoted to major of the 2nd Dragoons on June 30, 1846. During the Mexican–American War, Sumner was brevetted for bravery at the Battle of Cerro Gordo (to lieutenant colonel). It was here that he gained the nickname "Bull Head" because of a story about a musket ball that bounced off his head during the battle. At the Molino del Rey he received the brevet rank of colonel. He was promoted to lieutenant colonel of the 1st US Dragoons on July 23, 1848. He served as the military governor of the New Mexico Territory from 1851 to 1853 and was promoted to colonel of the 1st U.S. Cavalry on March 3, 1855. In 1856 Sumner commanded Fort Leavenworth, Kansas, and became involved in the crisis known as Bleeding Kansas. In 1857, as commander of the 1st Cavalry Regiment (1855), he led a punitive expedition against the Cheyenne, and in 1858 he commanded the Department of the West. On January 7, 1861, Sumner wrote to President-elect Abraham Lincoln, advising him to carry a weapon at all times. Lt. Gen. Winfield Scott assigned Sumner as the senior officer to accompany Lincoln from Springfield, Illinois, to Washington, D.C., in March 1861. Civil War In February 1861, Brig. Gen. David E. Twiggs was dismissed from the Army for treason by outgoing U.S. President James Buchanan, and on May 12, 1861, Sumner was nominated by the newly inaugurated Lincoln to replace Twiggs as one of only three brigadier generals in the regular army, with date of rank March 16. Sumner was thus the first new Union general created by the secession crisis. He was then sent to replace Brig. Gen. Albert Sidney Johnston, then in command of the Department of the Pacific in California, and thus took no part in the 1861 campaigns of the war. When Sumner left for California, his son-in-law Armistead Lindsay Long resigned his commission and enlisted with the Confederate Army eventually becoming Robert E. Lee's military secretary and an artillery brigadier general. In November 1861, Sumner was brought back east to command a division. When Maj. Gen. George B. McClellan began organizing the Army of the Potomac in March, Sumner was given command of one of its new corps. McClellan had not originally formed corps