Union General George B. McClellan spent the battle aboard the gunboat U.S.S. Galena

George B. McClellan, also known as "Little Mac," had traveled to the Virginia Peninsula in search of an American Waterloo—a significant battle that would conclude the war and make him the victor. However, the significant casualties of the current battles and the failure of the campaign, which had seemed so promising only a few days ago, left him feeling hopelessly dejected. The Union force was dispersed on the congested roads leading to Harrison's Landing on June 30, with each corps commander organizing his own evacuation and battle strategy.

To board the gunboat U.S.S. Galena on the James River, McClellan had ridden ahead of the army. McClellan dined and drank wine as the Galena steamed upriver. The lack of a strong leader in charge severely hurt the Union army at Glendale. The soldiers at Glendale were thrown together from several commands without the required command presence to properly react to enemy moves because McClellan failed to organize or oversee the army's retreat. The Union soldiers formed a crooked, disconnected line when they deployed, with the flanks of one unit not seamlessly joining the flank of another, creating a field of "bite-sized" pieces of the army. These isolated units would be in need of either a hasty withdrawal or immediate support when Lee's men emerged from the woods.