not renew the offensive. After dark, Lee ordered the battered Army of Northern Virginia to withdraw across the Potomac into the Shenandoah Valley. Shepherdstown On September 19, a detachment of Maj. Gen. Fitz John Porter's V Corps pushed across the river at Boteler's Ford, attacked the Confederate rear guard commanded by Brig. Gen. William N. Pendleton, and captured four guns. Early on September 20, Porter pushed elements of two divisions across the Potomac to establish a bridgehead. A.P. Hill's division counterattacked while many of the Federals were crossing and nearly annihilated the 118th Pennsylvania (the "Corn Exchange" Regiment), inflicting 269 casualties. This rearguard action discouraged further Federal pursuit. Aftermath and diplomatic implications Lee successfully withdrew across the Potomac, ending the Maryland campaign and summer campaigning altogether. President Lincoln was disappointed in McClellan's performance. He believed that the general's cautious and poorly coordinated actions in the field had forced the battle to a draw rather than a crippling Confederate defeat. He was even more astonished that from September 17 to October 26, despite repeated entreaties from the War Department and the president, McClellan declined to pursue Lee across the Potomac, citing shortages of equipment and the fear of overextending his forces. General-in-Chief Henry W. Halleck wrote in his official report, "The long inactivity of so large an army in the face of a defeated foe, and during the most favorable season for rapid movements and a vigorous campaign, was a matter of great disappointment and regret." Lincoln relieved McClellan of his command of the Army of the Potomac on November 7, effectively ending the general's military career. Maj. Gen. Ambrose E. Burnside rose to command the Army of the Potomac. The Eastern Theater was relatively quiet until December, when Lee faced Burnside at the Battle of Fredericksburg. Although a tactical draw, the Battle of Antietam was a strategic victory for the Union. It forced the end of Lee's strategic invasion of the North and gave Abraham Lincoln the victory he was awaiting before announcing the Emancipation Proclamation on September 22, which took effect on January 1, 1863. Although Lincoln had intended to do so earlier, he was advised by his Cabinet to make this announcement after a Union victory to avoid the perception that it was issued out of desperation. The Confederate reversal at Antietam also dissuaded the governments of France and Great Britain from recognizing the Confederacy. And, with the