The First Battle of Winchester, fought on May 25, 1862, in and around Frederick County, Virginia, and Winchester, Virginia, was a major victory in Confederate Army Maj. Gen. Thomas J. "Stonewall" Jackson's Campaign through the Shenandoah Valley during the American Civil War. Jackson enveloped the right flank of the Union Army under Maj. Gen. Nathaniel P. Banks and pursued it as it fled across the Potomac River into Maryland. Jackson's success in achieving force concentration early in the fighting allowed him to secure a more decisive victory which had escaped him in previous battles of the campaign.