Before the Battle of Chancellorsville, the Union Army had undergone a shakeup in command. General Ambrose Burnside, having lost the disastrous Battle of Fredericksburg the previous December, had been replaced by General Joseph Hooker. Hooker had spent the spring training his men to prepare for another face-off with Confederate troops. This time, he hoped to win. His goal was nothing less than the capture of the Confederate capital of Richmond, Virginia.

The numbers going into the Battle of Chancellorsville were on Hooker’s side: He commanded about 115,000 men, while Lee’s troops numbered just 60,000, perhaps the biggest Union advantage in the Civil War. Two divisions of the Confederate Army were absent, serving in Southern Virginia under General James Longstreet.

On April 27, 1863, after putting two-thirds of his forces in front of Fredericksburg to feign a frontal assault, Hooker led the other third of his Army of the Potomac across the Rappahannock River. He hoped to come up behind Confederate trenches near Fredericksburg and catch the enemy by surprise.

Hooker’s gambit was outdone by General Robert E. Lee’s quick thinking. Lee, too, divided his force, retaining 10,000 troops led by Jubal Early to hold Fredericksburg before marching the rest of his army West to meet Hooker head-on.

The two armies clashed in an open field just beyond the Wilderness, a forest west of Chancellorsville, on May 1, 1863. Despite his superior numbers, Hooker had his men fall back to defensive positions, opening the door for Lee to hatch the most brilliant offensive plan of his career.

Lee split his army again, sending his right-hand man Thomas J. “Stonewall” Jackson to attack the Union’s right flank, where they clashed with the Union XI Corps under Major General Oliver Otis Howard, caving in the Union line.

Lee and Jackson’s most celebrated victory also led to Jackson’s death. On May 2, Jackson marched his 28,000 troops nearly 15 miles to attack Hooker’s exposed flank, inflicting massive Union casualties. Half of Hooker’s forces were destroyed.

But Jackson’s victory would be his last. As the sun set, Jackson led his men to scout ahead in the forest. A North Carolina regiment opened fire, mistaking them for enemy cavalry. A bullet struck Jackson, shattering the bone above his left shoulder. General J. E. B. Stuart took over his command as doctors amputated Jackson’s left arm. While he was in a field hospital, Lee wrote to Jackson, “Could I have directed events, I would have chosen for the good of the country to be disabled in your stead.”

Jackson died from pneumonia on May 10, 1863. He was 39 years old. The South mourned their war hero, who was buried in Lexington, Virginia.

On May 3, 1863, a still-reeling Hooker found himself fending off attacks from General Lee himself.

Lee again outwitted him, moving on the rear of the 27,000 troops Hooker had left behind.

Between May 5 May 6, Hooker and his rain-soaked troops re-crossed the Rappahannock to beat a hasty retreat to Washington, D.C. He had lost 17,278 casualties to Lee’s 12,826.

Lee, now in a position of power even though he’d lost Jackson, would soon head north, where he’d again face off with Union troops in the Battle of Gettysburg.

President Abraham Lincoln, hearing of Hooker’s retreat, exclaimed, "My God! My God! What will the country say?”