On April 10, 1861, Brig. Gen. Beauregard, in command of the provisional Confederate forces at Charleston, South Carolina, demanded the surrender of the Union garrison of Fort Sumter in Charleston Harbor. Garrison commander Anderson refused. On April 12, Confederate batteries opened fire on the fort, which was unable to reply effectively. At 2:30 pm, April 13, Major Anderson surrendered Fort Sumter, evacuating the garrison on the following day. The bombardment of Fort Sumter was the opening engagement of the American Civil War. Although there were no casualties during the bombardment, one Union artillerist was killed and three wounded (one mortally) when a cannon exploded prematurely while firing a salute during the evacuation on April 14.
On September 16, 1862 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. Union assaults against the Sunken Road eventually pierced the Confederate center, but the Federal advantage was not followed up. Late in the day, Burnside's corps finally got into action, crossing the stone bridge over Antietam Creek and rolling up the Confederate right. At a crucial moment, A.P. Hill's division arrived from Harpers Ferry and counterattacked, driving back Burnside and saving the day. Although outnumbered two-to-one, Lee committed his entire force, while McClellan sent in less than three-quarters of his army, enabling Lee to fight the Federals to a standstill. During the night, both armies consolidated their lines. In spite of crippling casualties, Lee continued to skirmish with McClellan throughout the 18th, while removing his wounded south of the river. McClellan did not renew the assaults. After dark, Lee ordered the battered Army of Northern Virginia to withdraw across the Potomac into the Shenandoah Valley.
Gen. Robert E. Lee concentrated his full strength against Maj. Gen. George G. Meade's Army of the Potomac at the crossroads county seat of Gettysburg. On July 1, Confederate forces converged on the town from west and north, driving Union defenders back through the streets to Cemetery Hill. During the night, reinforcements arrived for both sides. On July 2, Lee attempted to envelop the Federals, first striking the Union left flank at the Peach Orchard, Wheatfield, Devil's Den, and the Round Tops with Longstreet's and Hill's divisions, and then attacking the Union right at Culp's and East Cemetery Hills with Ewell's divisions. By evening, the Federals retained Little Round Top and had repulsed most of Ewell's men. During the morning of July 3, the Confederate infantry were driven from their last toe-hold on Culp's Hill. In the afternoon, after a preliminary artillery bombardment, Lee attacked the Union center on Cemetery Ridge. The Pickett-Pettigrew assault (more popularly, Pickett's Charge) momentarily pierced the Union line but was driven back with severe casualties. Stuart's cavalry attempted to gain the Union rear but was repulsed. On July 4, Lee began withdrawing his army toward Williamsport on the Potomac River. His train of wounded stretched more than fourteen miles.
After the Tullahoma Campaign, Rosecrans renewed his offensive, aiming to force the Confederates out of Chattanooga. The three army corps comprising Rosecrans' s army split and set out for Chattanooga by separate routes. In early September 1863, Rosecrans consolidated his forces scattered in Tennessee and Georgia and forced Bragg's army out of Chattanooga, heading south. The Union troops followed it and brushed with it at Davis' Cross Roads. Bragg was determined to reoccupy Chattanooga and decided to meet a part of Rosecrans's army, defeat them, and then move back into the city. On the 17th he headed north, intending to meet and beat the XXI Army Corps. As Bragg marched north on the 18th, his cavalry and infantry fought with Union cavalry and mounted infantry which were armed with Spencer repeating rifles. Fighting began in earnest on the morning of the 19th, and Bragg's men hammered but did not break the Union line. The next day, Bragg continued his assault on the Union line on the left, and in late morning, Rosecrans was informed that he had a gap in his line. In moving units to shore up the supposed gap, Rosencrans created one, and James Longstreet's men promptly exploited it, driving one-third of the Union army, including Rosecrans himself, from the field. George H. Thomas took over command and began consolidating forces on Horseshoe Ridge and Snodgrass Hill. Although the Rebels launched determined assaults on these forces, they held until after dark. Thomas then led these men from the field leaving it to the Confederates. The Union retired to Chattanooga while the Rebels occupied the surrounding heights.