Lee then moved his troops northwards and split his men, sending Jackson to meet General John Pope’s Union forces near Manassas, while Lee himself moved separately with the second half of the army. On August 29, Union troops led by Pope struck Jackson’s forces in the Second Battle of Bull Run (Second Manassas).
The next day, Lee hit the Federal left flank with a massive assault, driving Pope’s men back towards Washington. On the heels of his victory at Manassas, Lee began the first Confederate invasion of the North. Despite contradictory orders from Lincoln and Halleck, McClellan was able to reorganize his army and strike at Lee on September 14 in Maryland, driving the Confederates back to a defensive position along Antietam Creek, near Sharpsburg.
Battle of Antietam
On September 17, the Army of the Potomac hit Lee’s forces (reinforced by Jackson’s) in what became the war’s bloodiest single day of fighting. Total casualties at the Battle of Antietam (also known as the Battle of Sharpsburg) numbered 12,410 of some 69,000 troops on the Union side, and 13,724 of around 52,000 for the Confederates.
The Union victory at Antietam would prove decisive, as it halted the Confederate advance in Maryland and forced Lee to retreat into Virginia. Still, McClellan’s failure to pursue his advantage earned him the scorn of Lincoln and Halleck, who removed him from command in favor of Ambrose E. Burnside.
Burnside’s assault on Lee’s troops near Fredericksburg on December 13 ended in heavy Union casualties and a Confederate victory; Burnside was promptly replaced by Joseph “Fighting Joe” Hooker, and both armies settled into winter quarters across the Rappahannock River from each other.
The Emancipation Proclamation
Lincoln used the occasion of the Union victory at Antietam to issue a preliminary Emancipation Proclamation, which freed all enslaved people in the rebellious states after January 1, 1863. He justified his decision as a wartime measure, and did not go so far as to free the enslaved people in the border states loyal to the Union.
Still, the Emancipation Proclamation deprived the Confederacy of the bulk of its labor forces and put international public opinion strongly on the Union side. Some 186,000 Black Civil War soldiers would join the Union Army by the time the war ended in 1865, and 38,000 lost their lives.
In the spring of 1863, Hooker’s plans for a Union offensive were thwarted by a surprise attack by the bulk of Lee’s forces on May 1, whereupon Hooker pulled his men back to Chancellorsville. The Confederates gained a costly victory in the Battle of Chancellorsville, suffering 13,000 casualties (around 22 percent of their troops); the Union lost 17,000 men (15 percent).
Battle of Gettysburg
Lee launched another invasion of the North in June, attacking Union forces commanded by General George Meade on July 1 near Gettysburg in Pennsylvania. Over three days of fierce fighting, the Confederates were unable to push through the Union center and suffered casualties close to 60 percent.
Meade failed to counterattack, however, and Lee’s remaining forces were able to escape into Virginia, ending the last Confederate invasion of the North. Also in July 1863, Union forces under Ulysses S. Grant took Vicksburg, Mississippi, after the brutal Siege of Vicksburg, a victory that would prove to be the turning point of the war in the western theater.
After a Confederate victory at Chickamauga Creek, Georgia, just south of Chattanooga, Tennessee, in September, Lincoln expanded Grant’s command, and he led a reinforced Federal army (including two corps from the Army of the Potomac) to victory in the Battle of Chattanooga in late November.