The Peninsula Campaign was a Union military operation in southeastern Virginia designed to strike at the Confederate capital of Richmond between March and July of 1862. It was led by General George B. McClellan and his Army of the Potomac, which numbered over 120,000 soldiers. McClellan's massive army moved via water on March 17, 1862, from Alexandria, Virginia to the Virginia peninsula, where McClellan besieged Yorktown in early May of 1862. McClellan vastly overestimated the size of Confederate forces defending Yorktown under Joseph Johnston and lost valuable time moving heavy artillery into place. Meanwhile, Confederate forces, realizing they could not hold Yorktown, escaped. Union forces would next engage the retreating Confederates on May 5, 1862, at Williamsburg, resulting in over 4,000 casualties and the continued Confederate withdrawal in the direction of Richmond. Union General McClellan continued the pursuit and ordered Brigadier General William Franklin and his army to board transport ships on the York River to cut off Johnston's escape.

On May 7th, 1862, Franklin's army was attacked by Confederates upon landing at Eltham's Landing, which prevented him from cutting off Johnston. Union forces nevertheless, continued to press on toward Richmond. On May 15, 1862, in what was likely the closest Union approach to the Confederate capital, Union naval vessels, including the ironclad USS Monitor, sailed up the James River toward Richmond and took massive fire from Confederate forces at Fort Darling, just seven miles from Richmond. In what came to be known as the Battle of Drewry's Bluff, the Union naval vessels were forced to withdraw. Confederate General Joseph Johnston withdrew his 60,000 man army in preparation to defend Richmond from an imminent attack.

Following Drewry's Bluff, Union forces under McClellan set up a several supply bases on the Pamunkey River and planned to use the region's railroad lines to bring his heavy artillery within range of Richmond. By May 18, McClellan had positioned 105,000 men northeast of Richmond, outnumbering Johnston's army of 60,000. Despite the huge advantage in manpower, McClellan was fooled into believing HE was outnumbered two to one by faulty intelligence. On May 27, in response to information that indicated a small Confederate force had moved into position at Hanover Courthouse, near the Union lines, McClellan dispatched Corps Commander Fitz John Porter to engage the enemy, where Union forces scored an insignificant victory.

Meanwhile, Confederate General Joseph Johnston, desperate to prevent a siege of the Confederate capital, preemptively attacked McClellan's army on May 31, 1862. In what came to be known as The Battle of Seven Pines (also called the Battle of Fair Oaks), Union and Confederate forces fought to a draw, although the Union advance on Richmond came to a screeching halt, as Confederate forces collapsed back to Richmond. Combined, the two sides suffered over 11,000 total casualties. Following the draw at Seven Pines, Confederate President Jefferson Davis replaced Johnston as Commander with Robert E. Lee. Lee immediately made plans to strengthen the defenses surrounding Richmond and to extend the defensive lines south of Richmond to Petersburg. On June 25, 1862, Lee launched a series of counterattacks on McClellan's Army that would cause McClellan to withdraw his army under withering fire south of the James River. These battles would collectively become known as the Battles of Seven Days and would result in 36,000 total casualties. Despite the heavy toll incurred by Confederate forces under Lee (20,000 casualties), he succeeded in driving McClellan's army away from Richmond. The Army of the Potomac would soon be recalled to Washington to support Union offensives in Northern Virginia. For now, the Confederate capital was safe.