The Gettysburg Campaign is a military invasion of Pennsylvania by the main Confederate army under General Robert E. Lee in summer 1863

The Union wins a decisive victory at Gettysburg July 1–3, with heavy casualties on both sides.

Lee manages to escape back to Virginia with most of his army

It is a turning point in the American Civil War, with Lee increasingly pushed back toward Richmond until his surrender in April 1865.

After his victory in the Battle of Chancellorsville, Lee's Army of Northern Virginia moves north for a massive raid designed to obtain desperately needed supplies, to undermine civilian morale in the North, and to encourage anti-war elements.

The Union Army of the Potomac is commanded by Maj. Gen. Joseph Hooker and then (from June 28) by Maj. Gen. George G. Meade.

Lee's army slips away from Federal contact at Fredericksburg, Virginia, on June 3, 1863.

The largest predominantly cavalry battle of the war is fought at Brandy Station on June 9.

The Confederates cross the Blue Ridge Mountains and move north through the Shenandoah Valley, capturing the Union garrison at Winchester, Virginia, in the Second Battle of Winchester, June 13–15.

Crossing the Potomac River, Lee's Second Corps advances through Maryland and Pennsylvania, reaching the Susquehanna River and threatening the state capital of Harrisburg.

However, the Army of the Potomac is in pursuit and has reached Frederick, Maryland, before Lee realizes his opponent has crossed the Potomac.

Lee moves swiftly to concentrate his army around the crossroads town of Gettysburg.

The Battle of Gettysburg is the largest of the war.

Starting as a chance meeting engagement on July 1, the Confederates are initially successful in driving Union cavalry and two infantry corps from their defensive positions, through the town, and onto Cemetery Hill.

On July 2, with most of both armies now present, Lee launches fierce assaults on both flanks of the Union defensive line, which are repulsed with heavy losses on both sides.

On July 3, Lee focuses his attention on the Union center.

The defeat of his massive infantry assault, Pickett's Charge, causes Lee to order a retreat that began the evening of July 4.

The Confederate retreat to Virginia is plagued by bad weather, difficult roads, and numerous skirmishes with Union cavalry.

However, Meade's army does not maneuver aggressively enough to prevent Lee from crossing the Potomac to safety on the night of July 13–14.