On November 1, 1861, President Abraham Lincoln names George Brinton McClellan general in chief of the Union army, replacing the aged and infirm Winfield Scott. In just six months, McClellan had gone from commander of the Ohio volunteers to the head of the Union army.

McClellan, a Pennsylvania native, graduated from West Point second in his class in 1846 and went on to serve with distinction under General Winfield Scott in the Mexican-American War (1846-48). McClellan left his successful military career in 1857 for an engineering position with the Illinois Central Railroad, and by the time the Civil War broke out in 1861, he was president of the St. Louis and Cincinnati Railroad. He resigned that position to accept command of the Ohio volunteers with the rank of major general.

During the summer of 1861, McClellan led Union troops in a series of small battles in western Virginia that resulted in Federal control of the strategic region. He earned a national reputation, though it is debatable just how much McClellan contributed to these achievements; in several cases, decisions by his subordinates were the main reason for the success. Nonetheless,McClellan provided Northern victories when they were in scarce supply. On July 16, 1861, the U.S. House of Representatives passed a resolution recognizing his accomplishments in Virginia.

Just five days later, the main Union force, commanded by General Irwin McDowell, suffered a humiliating defeat at the First Battle of Bull Run, Virginia. In the aftermath of the debacle, many turned to McClellan to save the war effort. He arrived in Washington, D.C., on July 26 to take command of the disorganized and demoralized Army of the Potomac and quickly began to build a magnificent fighting force, establishing a rigorous training procedure and an efficient command structure. He also demonstrated brashness, pomposity and arrogance toward many of the nation’s political leaders. He loudly complained about Scott, and treated the president with utter contempt.

Still,McClellan was the only real choice to replace Scott. No other Union general had achieved much of anything at that point in the war. After alienating much of the administration by early 1862, McClellan moved the Army of the Potomac to the James Peninsula for an attack on Richmond, Virginia. As a field commander, he proved to be sluggish and timid, and he retreated from the outskirts of the Confederate capital when faced with a series of attacks by Confederate General Robert E. Lee during the Seven Days Battles in June 1862.

In July, Henry W. Halleck was named general in chief, and much of McClellan’s Army of the Potomac was transferred to General John Pope’s Army of Virginia. After Pope was defeated at Second Bull Run in August, much of McClellan’s command was restored to him. Lee invaded Maryland, and McClellan defeated him there at the Battle of Antietam in September. Despite this victory, McClellan’s refusal to pursue the retreating Confederates led to his permanent removal in November 1862. In 1864, he challenged Lincoln for the presidency as the Democratic nominee but lost decisively.