Joseph Hooker in the context of "Eastern Theater of the American Civil War"

The Battle of Chancellorsville, April 30 – May 6, 1863, was a major battle of the American Civil War (1861–1865), and the principal engagement of the Chancellorsville campaign.

Confederate General Robert E. Lee's risky decision to divide his army in the presence of a much larger enemy force resulted in a significant Confederate victory, described by some historians as Lee's "perfect battle". The victory, a product of Lee's audacity and Union general Joseph Hooker's timid decision-making, was tempered by heavy casualties, including Lt. Gen. Thomas J. "Stonewall" Jackson. Jackson was hit by friendly fire, requiring his left arm to be amputated. He died of pneumonia eight days later, a loss that Lee likened to losing his right arm.

The Battle of Gettysburg (locally /ˈɡɛtɪsbɜːrɡ/ ) was a three-day battle in the American Civil War, which was fought between the Union and Confederate armies between July 1 and July 3, 1863, in and around Gettysburg, Pennsylvania. The battle, won by the Union, is widely considered the Civil War's turning point, leading to an ultimate victory of the Union and the preservation of the nation. The Battle of Gettysburg was the bloodiest battle of both the Civil War and of any battle in American military history, claiming over 50,000 combined casualties. Union Major General George Meade's Army of the Potomac defeated attacks by Confederate General Robert E. Lee's Army of Northern Virginia, halting Lee's invasion of the North and forcing his retreat.

After his success in the Battle of Chancellorsville in Spotsylvania County, Virginia in May 1863, Lee led his Confederate forces through Shenandoah Valley to begin the Gettysburg campaign, his second attempt to invade the North. With Lee's army in high spirits, he intended to shift the focus of the summer campaign from war-ravaged Northern Virginia in the hopes of penetrating as far as Harrisburg or Philadelphia, which he hoped would convince northern politicians to end the war. President Abraham Lincoln initially prodded Major General Joseph Hooker into pursuing Lee, then relieved him of command just three days before the Battle of Gettysburg commenced, replacing him with Meade.

The Gettysburg campaign was a military invasion of Pennsylvania by the main Confederate army under General Robert E. Lee in summer 1863. It was the first time during the war the Confederate Army attempted a full-scale invasion of a free state. The Union won a decisive victory at Gettysburg, July 1–3, with heavy casualties on both sides. Lee managed to escape back to Virginia with most of his army. It was a turning point in the American Civil War, with Lee increasingly pushed back toward Richmond until his surrender in April 1865. The Union Army of the Potomac was commanded by Maj. Gen. Joseph Hooker and then (from June 28) by Maj. Gen. George Meade.

After his victory in the Battle of Chancellorsville, Lee's Army of Northern Virginia moved north for a massive raid designed to obtain desperately needed supplies, to undermine civilian morale in the North, and to encourage anti-war elements. Lee's army slipped away from Federal contact at Fredericksburg, Virginia, on June 3, 1863. The largest predominantly cavalry battle of the war was fought at Brandy Station on June 9. The Confederates crossed the Blue Ridge Mountains and moved north through the Shenandoah Valley, capturing the Union garrison at Winchester, in the Second Battle of Winchester, June 13–15. Crossing the Potomac River, Lee's Second Corps advanced through Maryland and Pennsylvania, reaching the Susquehanna River and threatening the state capital of Harrisburg. However, the Army of the Potomac was in pursuit and had reached Frederick, Maryland, before Lee realized his opponent had crossed the Potomac. Lee moved swiftly to concentrate his army around the crossroads town of Gettysburg.

The Chattanooga campaign was a series of maneuvers and battles in October and November 1863, during the American Civil War. Following the defeat of Maj. Gen. William S. Rosecrans's Union Army of the Cumberland at the Battle of Chickamauga in September, the Confederate Army of Tennessee under Gen. Braxton Bragg besieged Rosecrans and his men by occupying key high terrain around Chattanooga, Tennessee. Maj. Gen. Ulysses S. Grant was given command of Union forces in the West which was now consolidated under the Division of the Mississippi. Significant reinforcements also began to arrive with him in Chattanooga from Mississippi and the Eastern Theater. On October 18, Grant removed Rosecrans from command of the Army of the Cumberland and replaced him with Major General George Henry Thomas.

During the opening of a supply line (the "Cracker Line") to feed the starving men and animals in Chattanooga, a force under Maj. Gen. Joseph Hooker fought off a Confederate counterattack at the Battle of Wauhatchie on October 28–29, 1863. On November 23, the Army of the Cumberland advanced from the fortifications around Chattanooga to seize the strategic high ground at Orchard Knob while elements of the Union Army of the Tennessee under Maj. Gen. William Tecumseh Sherman maneuvered to launch a surprise attack against Bragg's right flank on Missionary Ridge. On November 24, Sherman's men crossed the Tennessee River in the morning and then advanced to occupy high ground at the northern end of Missionary Ridge in the afternoon. The same day, a mixed force of almost three divisions under Maj. Gen. Joseph Hooker defeated the Confederates in the Battle of Lookout Mountain. The next day they began a movement toward Bragg's left flank at Rossville.