Battle of Chancellorsville, important engagement of the American Civil War (1861-1865) in which the Confederate Army used strategy to defeat a much larger Union force. The battle was fought on May 1 to 4, 1863, at Chancellorsville, an inn between Orange and Fredericksburg, Virginia. The Union forces, the federal Army of the Potomac, under General Joseph Hooker, numbered about 130,000; the Confederate forces, comprising the Army of Northern Virginia under General Robert E. Lee, numbered about 60,000.

In late April 1863 Hooker divided his forces, moving about 70,000 men to Chancellorsville. He also sent about 40,000 troops to threaten the Confederate defenses at Fredericksburg. Lee, however, responded to Hooker’s maneuvers by splitting his army as well. On the first day of May, Lee moved about 30,000 men under General Thomas “Stonewall” Jackson to attack the exposed right flank of Hooker’s army. This decision left about 15,000 Confederate troops to face Hooker’s main force at Chancellorsville with the remaining Confederate forces defending Fredericksburg.

On May 2, the Confederate corps under Jackson made a wide detour around the extreme right of Hooker’s fortified position at Chancellorsville to assault his flank. The purpose of this movement was not apparent to the Union forces. About 5:15 pm, after a march of some 19 km (some 12 mi), Jackson suddenly attacked and stampeded the flank and rear of the XI Corps, constituting the right flank of the Union army. However, this attack resulted in a major loss for the Confederate Army. Jackson, while in advance of his troops, was fired on and wounded by his own men, who mistook his escort for a detachment of Union soldiers. His left arm was amputated, and Jackson died eight days later.

During this movement Lee made a series of successful diversionary attacks on Hooker’s frontal positions, thus immobilizing the bulk of the Union Army. On the morning of May 3 Lee vigorously attacked the Union front and flank, with Jackson’s force, commanded by General J. E. B. Stuart. The brunt of the assault fell on units under General Daniel Edgar Sickles, on the Union right, and General Henry Warner Slocum, at the center. Hooker showed indecision, and the Union Army withdrew to strong defensive positions. Lee was deterred from immediately following up his advantage by the news that his position was threatened on the right by an advance of a Union force under General John Sedgwick. Confederate reinforcements, however, checked Sedgwick’s advance on May 3rd and 4th, and Lee then prepared to advance against Hooker, but Hooker hastily withdrew his army back across the Rappahannock River during a heavy storm.

The Confederates had managed to defeat a force over twice their size. Their victory frustrated Union plans for an assault on Richmond, the capital of the Confederacy, and made possible Lee’s subsequent invasion of the North, resulting in the Battle of Gettysburg. Union casualties totaled about 17,300; Confederate losses were about 12,750.