troops. Emboldened by Second Bull Run, the Confederacy made its first invasion of the North with the Maryland Campaign. General Lee led 45,000 troops of the Army of Northern Virginia across the Potomac River into Maryland on September 5. Lincoln then restored Pope's troops to McClellan. McClellan and Lee fought at the Battle of Antietam near Sharpsburg, Maryland, on September 17, 1862, the bloodiest single day in United States military history. Lee's army, checked at last, returned to Virginia before McClellan could destroy it. Antietam is considered a Union victory because it halted Lee's invasion of the North and provided an opportunity for Lincoln to announce his Emancipation Proclamation. When the cautious McClellan failed to follow up on Antietam, he was replaced by Maj. Gen. Ambrose Burnside. Burnside was soon defeated at the Battle of Fredericksburg on December 13, 1862, when more than 12,000 Union soldiers were killed or wounded during repeated futile frontal assaults against Marye's Heights. After the battle, Burnside was replaced by Maj. Gen. Joseph Hooker. Hooker, too, proved unable to defeat Lee's army; despite outnumbering the Confederates by more than two to one, his Chancellorsville Campaign proved ineffective and he was humiliated in the Battle of Chancellorsville in May 1863. Chancellorsville is known as Lee's "perfect battle" because his risky decision to divide his army in the presence of a much larger enemy force resulted in a significant Confederate victory. Gen. Stonewall Jackson was shot in the arm by accidental friendly fire during the battle and subsequently died of complications. Lee famously said: "He has lost his left arm, but I have lost my right arm." The fiercest fighting of the battle—and the second bloodiest day of the Civil War—occurred on May 3 as Lee launched multiple attacks against the Union position at Chancellorsville. That same day, John Sedgwick advanced across the Rappahannock River, defeated the small Confederate force at Marye's Heights in the Second Battle of Fredericksburg, and then moved to the west. The Confederates fought a successful delaying action at the Battle of Salem Church. Gen. Hooker was replaced by Maj. Gen. George Meade during Lee's second invasion of the North, in June. Meade defeated Lee at the Battle of Gettysburg (July 1 to 3, 1863). This was the bloodiest battle of the war and has been called the war's turning point. Pickett's Charge on July 3 is often considered the high-water mark of