In March 1862, Union forces commanded by Major General Nathaniel P. Banks moved into the Shenandoah Valley with the goal of supporting Major General George B. McClellan's advance up the Virginia Peninsula. Confederate resistance to Banks' advance consisted of a small army commanded by Major General Thomas J. "Stonewall" Jackson. On March 21, the Union high command ordered the majority of Banks' command out of the Shenandoah Valley, leaving only a division commanded by Brigadier General James Shields to deal with Jackson. Shields left his camp at Strasburg and began moving north towards Winchester. On March 23, Jackson caught up with Shields' division near Kernstown. Faulty intelligence led Jackson to believe that only a small portion of Shields' force was at Kernstown, so he ordered an assault. Instead, Shields was in the area with his entire force, and a sharp battle was opened. The Confederates took a position behind a stone wall, but after Confederate Brigadier General Richard B. Garnett's brigade retreated after running low on ammunition, the flank of the Confederate position was exposed, forcing Jackson to withdraw from the field. Despite having defeated Jackson at Kernstown, Union high command was concerned by the aggressive behavior the Confederate army had shown, and began to send more troops to the Shenandoah Valley area, including the two divisions of Banks' army that had been moved out earlier.