After the fiasco at Bull Run, Union General McClellan had insisted that his army be thoroughly trained before sent into action.  By April 1862, however, Lincoln had grown tired of watching his army drill around the outskirts of Washington and pressed McClellan to launch a campaign against Richmond.  McClellan reluctantly agreed, but only after winning approval for his route to the Confederate capital.  Lincoln would have preferred an overland march through Manassas; this would ensure that McClellan’s army stayed between the Confederate army and Washington, D.C.  McClellan wanted to ferry his troop to the mouth of the Chesapeake and approach Richmond from the southeast.  This simplified the march but left the North’s capital exposed.  As a compromise, McClellan agreed to leave 40,000 troops behind to protect the city.

The 90,000 men McClellan took with him might have been enough had they moved on Richmond quickly.  But upon reaching the mouth of the Chesapeake, he was outfoxed by Confederate Major General John Magruder.  Magruder only had 15,000 men with him at Yorktown barring McClellan’s advance.  But he paraded them around visibly and repeatedly. Apparently, to McClellan, every Southerner looked the same, for he concluded that Magruder’s force was much stronger.  He therefore waited until his entire army had arrived and his big guns were deployed, at which point the Confederates simply retreated toward Richmond, having delayed McClellan a full month.

Meanwhile, further to the north, Bull Run hero Stonewall Jackson detained another force originally marked to support McClellan’s Richmond campaign.  Jackson’s army numbered only 8000; Union Generals Nathaniel Banks and John C. Fremont had more than 30,000.  But Jackson ran circles around the two Union generals, tying up their troops and convincing folks in Washington that an assault on the Northern capital was coming.  As a result 20,000 troops from General Mc Dowell’s army, originally destined for Richmond, were split off to defend Washington.

The bottom line: by the time McClellan moved on Richmond he had 100,000 troops rather than the 150,000 he had wanted. And Confederate Generals Joe Johnston and Robert E. Lee had managed to collect a force of almost 90,000 during the delayed Northern advance.  Perhaps just as important, J.E.B. Stuart’s collected precise intelligence of Northern positioning by leading his cavalry on a daring ride around the Union army. 

Still, the Union force was an intimidating thing.  Deployed like giant pincers along both side of the Chickahominy River, the Union Army seemed poised to squeeze the Confederate capital into submission.   But Lee, leaving about 20,000 troops behind to protect the city, concentrated his forces and probed weak spots in the Northern lines between 26 June and 1 July.  First he attacked at Mechanicsville, then at Gaines’ Mill, Savage’s Station, Frayser’s Farm, and Malvern Hill.

The Seven Days Battle took a terrible toll on both armies. Assuming the offensive throughout the week, Lee’s army suffered close to 20,000 casualties.  But the Union army lost more than 16,000 men. More important, after the fighting at Malvern Hill, McClellan abandoned his plans to seize Richmond.  He withdrew down the peninsula to the protection of his gun boats anchored in the James River.