In November 1861, President Abraham Lincoln named George B. McClellan to replace the aging Winfield Scott as general in chief of all Union armies. A rising star in the U.S. Army before the war, the West Point-educated McClellan had been summoned to Washington after the Union’s devastating defeat at Bull Run (Manassas) the previous July and had since managed to shape the mass of inexperienced volunteer troops into a disciplined fighting force, known as the Army of the Potomac.

Though much loved by his men, McClellan was deliberate and cautious in the extreme, and from early in the conflict he consistently overestimated the strength of Confederate troops facing him. Lincoln soon grew frustrated with McClellan’s reluctance to take the initiative, and in late January 1862 he issued General War Order No. 1, calling for all armies to move forward.

Issuing a long list of objections to the president’s plan, McClellan persuaded the skeptical Lincoln to further postpone the offensive against Joseph E. Johnston’s Confederate army, then stationed at Manassas in northern Virginia (scene of July’s defeat). Instead of an overland offensive, McClellan wanted to move his army by boat down the Chesapeake Bay to the mouth of the Rappahannock River and get in between Johnston’s army and the Confederate capital of Richmond. In early March, Lincoln approved this plan (provided enough troops were left behind to safeguard Washington) but removed McClellan as the Union general in chief, leaving him in command only of the Army of the Potomac.

Even as McClellan won approval for his planned offensive, Johnston withdrew his army from Manassas to a more easily defensible position at Culpeper, some 40 miles south and on the other side of the Rappahannock. The Union Army’s inspection of the abandoned Confederate works revealed that the enemy’s defenses had been far weaker than McClellan had claimed. In particular, a number of the Confederate cannons were found to be only logs painted black, known as “Quaker guns.” From then on, McClellan’s continued demands for more troops to face a superior enemy force would fall on deaf ears in Washington.

Foiled by Johnston’s move, McClellan now sought to move his Army of the Potomac by boat to Fort Monroe, located at the tip of the peninsula formed by the York and James Rivers in Virginia. From there, the army would move up the peninsula towards Richmond, forcing Johnston to move quickly south to defend the Confederate capital. Lincoln and Secretary of War Edwin M. Stanton agreed reluctantly. After finding that McClellan had not complied with the president’s order to leave enough troops to defend Washington, they ordered an entire large corps held back from the advance, and a furious McClellan traveled to Fort Monroe with some 100,000 troops instead of the 150,000 he had wanted.

By early April, 60,000 of McClellan’s soldiers were facing Confederate lines near Yorktown, Virginia, defended by some 13,000 rebels. Though the bulk of Johnston’s army was some 80 miles away, McClellan continued to wait, defying Lincoln’s repeated orders to attack. On May 4, Johnston decided to pull his troops from Yorktown and withdraw them toward Richmond, and McClellan finally ordered his army to move up the peninsula. By the third week of that month, the Army of the Potomac was approaching the Confederate capital. Though he was leading more than 100,000 Federals against 60,000 rebel defenders, McClellan continued to call for reinforcements.

On May 31, Johnston led Confederates in an attack against two Federal corps south of the Chickahominy River, six miles east of Richmond. In the two-day Battle of Seven Pines and Fair Oaks, the rebels were able to drive back one Union corps and inflict heavy casualties before the Federals (with the help of reinforcements) stabilized their line. General Johnston was seriously injured in the battle, and President Jefferson Davis replaced him with Robert E. Lee, a move that would have profound consequences for the rest of the conflict.

Through most of June, as Lee prepared a counteroffensive, McClellan complained to Washington of his need for more supplies and reinforcements. He claimed to be facing some 200,000 enemy troops; in reality, the maximum strength of Lee’s forces was around 92,000. Leaving some divisions to defend Richmond, Lee attacked McClellan’s right flank north of the Chickahominy (around 30,000 Federals) with an army of some 85,000 on July 26. During the seven days that followed, the Confederate general ordered repeated attacks: at Mechanicsville, Gaines’ Mill, Savage’s Station, Frayser’s Farm, Malvern Hill and many smaller skirmishes.