One hundred sixty years ago today, a savage dawn to dusk battle occurred in the rolling countryside of western Maryland.  The great Civil War historian, Bruce Catton, wrote that the Battle of Antietam produced, “the decisive victory of the warone [sic] of the great, decisive victories in American history.”

By the late summer of 1862, prospects for preservation of the Union looked bleak.  The Federal campaign to control the Mississippi River had floundered, and the Confederates were invading Kentucky and Maryland.  Great Britain and France readied to recognize the Confederacy.

The invasion of Maryland by the Army of Northern Virginia posed the gravest threat to the Union.  Under the command of General Robert E. Lee, this army in midsummer threw back the attempt to take Richmond, and in late August, routed Union forces at the Second Battle of Bull Run.

General Lee now sought a decisive victory on Union soil.  He and his army believed they could whip any Union force sent against them.  Lee especially believed he could defeat General George B. McClellan, the overly cautious (and delusional and paranoid) commander of the Army of the Potomac.  Lee had come close to destroying this army outside Richmond.

By great fortune, Confederate campaign plans fell into McClellan’s possession on September 13, when McClellan (commanding over 85,000 men) had advanced to Frederick, Maryland.  At the time, Lee’s army of 41,000 men was widely scattered.  As a precaution Lee had posted small blocking forces at the gaps in South Mountain, a mountain ridge twelve miles west of Frederick.

Knowing Lee’s plans gave McClellan the confidence to quickly move against the gaps.  On September 14, McClellan drove the Confederates from South Mountain.

But rapidity by “The Young Napoleon” could last only so long.  McClellan returned to advancing cautiously.  He believed Lee had 120,000 men under his command.  This delusion — which so grievously hampered McClellan outside Richmond — would now befoul his decisions at Antietam.

McClellan’s advance forced Lee to try to concentrate his army before Union forces could defeat them in detail.  Lee commanded his units to make for the town of Sharpsburg, adjacent to Antietam Creek, which lay about five miles west from South Mountain.

Lee had chosen a good, but not ideal defensive position.  He had placed his army with its back to the Potomac River, and only one fordable exit was available for retreat.  Furthermore by the morning of September 16, Lee’s army was still not fully concentrated.  General A.P. Hill’s division remained at Harpers Ferry, seventeen miles away, and two other of Stonewall Jackson’s divisions were en route.

McClellan threw away September 16, when he had over 73,000 men available to attack while Lee had no more than 25,000 at hand.  Lee’s lines would have probably cracked like an eggshell.  The Army of Northern Virginia, heart and soul of the Confederacy, would have been taken off the board.  Along with its stellar commanders of Lee, Jackson, Stuart, and Longstreet.

The Young Napoleon finally attacked at dawn on September 17.  That morning, Lee had 37,000 men present.  A dreadful three-act play ensued.

Act I (early morning) involved the Miller cornfield, the Dunker Church, and woodland on the northern side of the battlefield.  Unbelievably fierce fighting resulted in over 10,000 casualties.  Union forces came close to breaking Jackson’s line, but McClellan committed his divisions piecemeal.  This allowed Lee and Jackson to beat back each attack separately.

Act II (mid morning) involved a sunken country lane in the center of the battlefield.  The dirt farm road provided a natural fortress for the Confederates and allowed them to mow down attack after Union attack.  Blue clad bodies piled up on the field before the lane.

Union troops finally flanked the lane and their enfilade fire returned the favor of slaughter.  The enfilade fire and a misunderstood command caused the surviving Confederates to abandon the lane.  (The corpse-filled stretch ever after was known as “The Bloody Lane”.)

Now came a moment of supreme opportunity.  The Confederate center was broken.  No reserves remained for Lee.  The Confederates were reduced to generals manning field pieces and wielding muskets.

McClellan had 30,000 uncommitted men available to administer the coup de grace.  He hemmed and hawed.  Incredibly he was worried about a massive Confederate counterattack.  In the end, Young Napoleon did nothing.

Act III (afternoon) involved an arched stone bridge over Antietam Creek on the southern end of the battlefield.  General Ambrose Burnside was tasked with carrying the bridge (later named for him) and attacking Lee’s denuded right wing.  The first two assaults on the bridge failed.  Early afternoon, the whiskey inspired men of two regiments took the bridge and the overlooking bluff.  Another attack succeeded crossing further downstream.

Again ignoring the military dictum “reinforce success”, McClellan did not send in his reserves.  For a while it looked like Burnside (who McClellan despised and mistrusted) would not need help.  Against desperate but badly outnumbered opposition his corps steadily advanced towards Sharpsburg and the vital Boteler's Ford.  If Burnside reached the ford, Lee’s army was trapped.

On this day of outlandish drama, Act III properly closed with the most far-fetched scene of all.  Driven by the sword prodding General A. P. Hill, a Confederate division, completed their forced march from Harpers Ferry.  With complete surprise the division smashed into the flank of Burnside’s corps and drove it back to the arched bridge.  At the last second, Union victory was snatched away.

Sunset blessedly brought an end to the carnage.  Over twenty-two thousand Americans had been killed or wounded (the highest single day toll, before or since, in the nation's history).  But as the sound of battle faded away, the survivors became all too aware of other noise.  The cries of the wounded filled the night air.

McClellan (who should have been hung from a sour apple tree) did not attack the next day, although his army now outnumbered the battered Army of Northern Virginia two and a half to one.  During the night, Lee withdrew to Virginia.

Tactically, the Battle of Antietam was a draw.  Yet the battle, however botched, proved a strategic victory for the Union —  and for the beleaguered Lincoln Administration.  Lee’s invasion of Maryland had been repelled, and the threat of foreign intervention reduced.

An act of ultimately far greater importance took place five days later.  President Lincoln issued the Emancipation Proclamation, which on January 1, 1863, would outlaw slavery in Confederate-held territory.  It also allowed Blacks to join the Union army.  Lincoln had waited since July for a Union victory, any victory, to make the proclamation.

The proclamation fundamentally changed the Union cause. As Bruce Catton wrote:

It finally determined that the Civil War was not merely a war for reunion but also a war to end human slavery; turned it from a family scrap into an incalculable struggle for human freedom, and thus made it a fight in which no civilized outsider could possibly intervene.

Such became the abiding legacy of the slaughterhouse Battle of Antietam.

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