When Union forces discovered the battle plans of Robert E. Lee for his first invasion of the North on September 13, 1862, it offered Union general George McClellan the chance that all military commanders dream of—he knew the enemy’s plans in advance. He knew where Lee’s troops were and, furthermore, that Lee had split his army into fragments while on the march. It was a golden opportunity to destroy Lee’s army piece by piece. The discovery of Lee’s battle plans at Antietam should have ended the Civil War a little more than a year after it began.
Yet, as we know, that’s not what happened. McClellan moved too slowly. His unfortunate tendency to overestimate the number of Lee’s troops proved his undoing, and he did not join battle until Lee’s entire Army of Northern Virginia had assembled near Antietam Creek in Maryland. The battle itself, one continuous and horribly bloody day of fighting, was indecisive, but Lee departed the field afterward and returned to Virginia. This allowed Union forces to claim a victory, however modest.
Was the discovery of Lee’s Battle Plans at Antietam a Disaster or Blessing in Disguise?
The answer to this question probably seems self-evident. McClellan, despite having Lee’s battle plans at Antietam, lost the best chance the Union had to win the war early. The Civil War ended up lasting until 1865 and killing more than 600,000 people. How could McClellan’s indecision have been anything other than a disaster?
To answer this, consider what would’ve happened if McClellan had defeated Lee and ended the war in 1862. I know we’re playing counterfactual history here, so I’ll stick to the obvious things. The most notable involves the slavery issue. Most historians will tell you the silver lining of Antietam for the Union was that it resulted in Abraham Lincoln issuing the Emancipation Proclamation, which went into effect on January 1, 1863.
Contrary to what you may have learned, the Emancipation Proclamation was not a humanitarian act at its core. It was, primarily, a military move. Slaves freed up more Southern soldiers to fight by growing food, hauling supplies, and so forth. They aided the Confederate war effort. One way to disrupt that war effort was to encourage slaves to desert and head for Union lines by offering them freedom.
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Why this Matters
I think this is critical. If McClellan, knowing Lee’s battle plans at Antietam, had won a decisive victory by attacking aggressively, the Emancipation Proclamation never happens because there is no need for it. The Civil War probably ends shortly after Antietam, but with slavery still intact. The Southern states return to the nation, chastised and humbled, but without the fundamental alteration of Southern society produced by Emancipation and the end of slavery.
Where things go after this is harder to say. However, it’s not at all certain that the Thirteenth Amendment to the US Constitution happens without Emancipation, at least not in 1865. How long would the US have taken to get rid of slavery at that point? No one can say but imagine the horror of slavery stretching several decades into the future beyond 1862.
So, when I teach about this episode from the Civil War, I try to describe McClellan’s discovery of Lee’s battle plans at Antietam as both fortuitous and disastrous at the same time.
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