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. or
Levin C. Handy 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 within the Army; Sumner was selected as one of four corps commanders by President Lincoln, based on his seniority. The
II Corps, commanded during the war by Sumner,
Darius N. Couch,
Winfield Scott Hancock, and
Andrew A. Humphreys, had the deserved reputation of being one of the best in the
Eastern Theater. Sumner, who was the oldest of the generals in the Army of the Potomac, led his corps throughout the
Peninsula Campaign and the
Seven Days Battles. McClellan originally formed a poor opinion of Sumner during the
Battle of Williamsburg on May 5, 1862. During McClellan's absence, Sumner directed the inconclusive battle, which failed to impede the Confederate withdrawal up the Peninsula, and McClellan wrote to his wife, "Sumner had proved that he was even a greater fool than I had supposed & had come within an ace of having us defeated." At the
Battle of Seven Pines, however, Sumner's initiative in sending reinforcing troops across the dangerously rain-swollen
Chickahominy River prevented a Union disaster. He received the brevet of major general in the regular army for his gallantry at Seven Pines. Sumner was struck in the arm and hand by spent balls at the
Battle of Glendale. Despite his old-fashioned ideas on discipline and respect for commanding officers, the II Corps troops generally had a positive opinion of him. Sumner was promoted to major general of volunteers on July 4, 1862, with the rank dated to May 5. In the fall of 1862, at the
Battle of Antietam, Sumner was the center of controversy for ordering Brig. Gen.
John Sedgwick's division to launch an attack into the West Woods on the morning of the battle. The assault was devastated by a Confederate counterattack, and Sedgwick's men retreated in great disorder to their starting point with over 2,200 casualties. Sumner has been condemned by most historians for his "reckless" attack, his lack of coordination with the other corps commanders, accompanying Sedgwick's division personally and losing control of his other attacking division, failing to perform adequate reconnaissance prior to launching his attack, and selecting an unusual line of battle formation that was so effectively flanked by the Confederate counterattack. Historian M. V. Armstrong's recent scholarship, however, has determined that Sumner did perform appropriate reconnaissance and his decision to attack where he did was justified by the information available to him. Sumner's other divisions drove the weak Confederate center back, but Sumner was badly shaken by the disaster to Sedgwick and heavy casualties to other Union forces. Maj. Gen.
William B. Franklin wanted to attack with his fresh VI Corps, but Sumner, who was senior to him, ordered him to hold back. McClellan sustained Sumner. Shortly before being fired from command of the army in October, McClellan wrote to the War Department a letter recommending that Sumner be relieved of duty, as he doubted that his age and health would permit him to survive another campaign, but nothing came of this and when Maj. Gen.
Ambrose Burnside succeeded to the command of the Army of the Potomac, he grouped the corps in "grand divisions" and appointed Sumner to command the Right Grand Division. In this capacity, he took part in the disastrous
Battle of Fredericksburg, in which the II Corps, now commanded by Major General
Darius N. Couch, suffered heavy casualties in frontal assaults against Confederate troops fortified at
Marye's Heights. Before that, Sumner went to his daughter's home in
Syracuse, New York, to rest, where he fell ill with fever. He died on March 21, 1863, and was buried in Syracuse's Oakwood Cemetery. His two sons, Brigadier General
Edwin Vose Sumner, Jr. and Major General
Samuel S. Sumner, both served in the Civil War and the
Spanish–American War. ==Grave==