Wednesday, September 17, produced the largest one-day bloodbath on American soil. From sunrise until dusk Federal units made repeated assaults on Lee’s lines. Had McClellan thrown his entire army against Lee’s position, the weight of numbers probably would have destroyed the Army of Northern Virginia. Instead, the Federal commander shifted his attacks from one sector to another. Casualties mounted frightfully in such areas as the East Wood, West Wood, Dunker Church, Sunken Road, and around Burnside’s Bridge. By nightfall Lee’s battered army still held its position. McClellan had lost 12,000 men, the Confederates 9,000. The battle of Antietam Creek ended Lee’s invasion, and he retired to Virginia. Five days after the engagement, Lincoln issued his preliminary Emancipation Proclamation. This document promised freedom to all slaves in Confederate-held territory after January 1, 1863. As such, it converted the war into a struggle for human freedom and deterred European nations from granting aid or recognition to the Confederacy. Many historians therefore maintain that Antietam Creek and its aftermath were the turning points of the Civil War. For six weeks after Antietam, McClellan seemed to make little effort to resume the campaign against Lee. Lincoln tired of waiting; on November 5 he replaced McClellan with Gen. Ambrose E. Burnside. [Illustration: Fredericksburg, viewed from Federal gun emplacements north of the city. The battle occurred on the heights in the left background.] “I am not competent to command such a large army,” Burnside stated. He demonstrated this truth in his one battle at the head of the Army of the Potomac. On December 13, a freezing Saturday, Burnside ordered six grand assaults against Lee’s entrenched army on the heights overlooking Fredericksburg, Va. The result was a useless slaughter, and a defeated Burnside wept over the killing and wounding of 10,000 of his men. Confederate losses were less than half that number. A few weeks later Burnside attempted a secret march around Lee’s left (western) flank. The Federal army bogged down in winter mud and made barely a mile a day. This “Mud March” finished Burnside. He soon relinquished command to Gen. Joseph Hooker, a strong-willed officer known to the soldiers as “Fighting Joe.” 1863 IN THE WEST Cavalry raids by both sides occupied the early months of this third year of conflict. One of the longest was that of Col. Benjamin H. Grierson and 17,000 Federal horsemen. Leaving La Grange, Tenn., in April, Grierson’s troopers wrecked railroads and supply depots all the way to Baton Rouge, La. The raid lasted two weeks and helped clear the way for Grant’s campaign against Vicksburg.