On September 17, 1862, the single bloodiest day of the Civil War, the Army of the Potomac under George B. McClellan clashed with Lee's invading Army of Northern Virginia at Antietam Creek. General Francis W. Palfrey (1831–1889), then lieutenant colonel of the 20th Massachusetts and later a founding member of the Military Historical Society of Massachusetts, was severely wounded in the savage struggle that forced the Confederates to retreat across the Potomac. The Union victory, though costly and indecisive, was sufficient for Lincoln to issue the Emancipation Proclamation. Less than three months later, the Battle of Fredericksburg (where droves of Union soldiers were slaughtered) ended the year with a resounding, grisly defeat.The Antietam and Fredericksburg (1882), is invaluable for Palfrey's unique eyewitness perspective; his unsparing, provocative appraisals of Generals McClellan, Burnside, Hooker, and others; his careful, detailed description of the Antietam terrain (vastly altered over time); and his incisive analyses of the folly and fighting that determined two of the most pivotal, murderous battles of the Civil War.