On September 16, Maj. Gen. George B. McClellan confronted Lee’s Army of Northern Virginia at Sharpsburg, Maryland. At dawn September 17, Hooker’s corps mounted a powerful assault on Lee’s left flank that began the single bloodiest day in American military history. Attacks and counterattacks swept across Miller’s cornfield and fighting swirled around the Dunker Church.

On July 8, the Confederate cavalry, holding the South Mountain passes, fought a rearguard action against elements of the Union 1st and 3rd Cavalry Divisions and infantry. This action was one of a series of cavalry combats fought around Boonsboro, Hagerstown, and Williamsport.

After burning Chambersburg, Pennsylvania, on July 30, Johnson’s and McCausland’s cavalry brigades rode towards Cumberland, Maryland, to disrupt the B&O Railroad. Brig. Gen. Benjamin Kelly organized a small force of soldiers and citizens to meet the Confederate advance.

On January 1, Maj. Gen. Thomas J. “Stonewall” Jackson marched north in bitter cold from Winchester to Bath with the objective of disrupting traffic on the B&O Railroad and C&O Canal. On January 5, after skirmishing with the retiring Federals, Jackson’s force reached the Potomac River opposite the garrisoned town of Hancock, Maryland.

After marching north through the Shenandoah Valley from Lynchburg, the Confederate army of Lt. Gen. Jubal A. Early side-stepped the Federal garrison at Harpers Ferry and crossed the Potomac River at Shepherdstown into Maryland on July 5-6. On July 9, 1864, a makeshift Union force under Maj. Gen. Lew Wallace attempted to arrest Early’s invading Confederate divisions along the Monocacy River, just east of Frederick.

After invading Maryland in September 1862, Gen. Robert E. Lee divided his army to march on and invest Harpers Ferry. The Army of the Potomac under Maj. Gen. George B. McClellan pursued the Confederates to Frederick, Maryland, then advanced on South Mountain.

During the night of July 4-5, Lee's battered army began its retreat from Gettysburg, moving southwest on the Fairfield Road toward Hagerstown and Williamsport, screened by Stuart’s cavalry. The Union infantry followed cautiously the next day, converging on Middletown, Maryland. On July 7, Imboden (CS) stopped Buford’s Union cavalry from occupying Williamsport and destroying Confederate trains.