I've brought this up before to old-school American History buffs, who pounce on the idea that Gettysburg or Antiedam might have gone the other way, and this would have led to some sort of capture of Washington or something. So my question to you is, what exactly would a "capture of DC" entail? I've heard that it was the most heavily defended city in the world at the end of the war, I assume there were significant forces in reserve during those engagements to garrison the capital? I assume Lincoln was in the White House during the war, would he be expected to flee, and then who cares what happens to the city? Or could there be some sort of hostage scenario, execution of The Tyrant, or whatever? TELL ME WHAT YOU KNOW.
Yes, the capital was the most heavily defended place in the world at the time. By 1870, the Paris system of fortifications would be far more formidable, but that was still some way off; the only other comparable city I can think of would be Taiping Nanjing, but Zeng Guofan's Hunan Army stormed it in 1864 so. In order to successfully assault the capital, Lee would have to have his forces fight through the very large capital-area garrison, somehow smash the cordon of forts in the suburbs at the same time, all the while defending against whatever Federal armies would be shipped in to attack his rear or reinforce the capital.
Good luck with that, Zombie Bobby.
The Confederates' best chance at capturing DC was in the first year of the war, before the outskirts of the city became a massive network of entrenchments and fortifications. Any long siege by the Confederates would be matched by the Union funneling massive amounts of manpower into the defense and counterattacks (look at how quickly Stanton moved troops to Tennessee to reinforce after Chickamauga--in 8 days, I think, they were able to move 25,000 troops from Virginia all the way to Chattanooga). Reinforcing DC would be an even greater priority, and they would have the massive rail networks of the East dumping troops off in Maryland and marching up to the lines.
I think any Confederate assault on DC after Gettsyburg (or even after Antietam) would result in a massive battle of attrition that would only magnify the Confederate's manpower and supply problems in the East.
Ignoring that, though, one has to look at the operational ramifications of attacking Washington at all.
First and foremost, Lee was fundamentally uninterested in attacking the capital for the very salient reason that he thought his army was too small for it, lacked the firepower, and would ultimately lose and gain nothing out of the project. So there's that to consider; the only way this stops being relevant is if for whatever reason the capital's forces are ever reduced, and the only time Lincoln even considered doing that was when Grant asked for more troops in the Overland Campaign. (This led to Early's march, the Battle of Monocacy Creek, and the very apparent fact that even when the so-called "heavy" regiments were sent to serve with the Army of the Potomac, the capital was still more than adequately defended.)
Secondly, the actual campaigns surrounding Antietam and Gettysburg militate very strongly against either being used to springboard an attack by the ANV on the DC fortifications. Antietam was not supposed to be a battle at all, it was a way for Lee to cover his army's
withdrawal into Virginia after finding that Maryland had little forage and even fewer recruits than he had thought. If McClellan had not gotten a receipt of the so-called Lost Orders, he simply would have missed Lee entirely and been forced to deal with the Confederates in Virginia instead. Knowing McClellan, he would have chosen the option of
not dealing with them, so.
Anyway. A colossal victory for the ANV was simply not in the cards at Antietam. Lee's objective was to unite his army as rapidly as possible, prevent any individual part of it from being overwhelmed, and escape. Nothing else was even remotely plausible: he did not want to attack the Army of the Potomac, because he believed he would lose a force-on-force clash if he did so, and he
certainly did not want to do that with only half of his army (Jackson's corps being stuck at Harper's Ferry until the very eve of the battle). The
best reasonable outcome of the battle was precisely what Lee got: a tactical stalemate, a failure by the Federals to press their advantages of concentration in space and time, and a successful retreat into Virginia. Antietam was a Confederate victory in every meaningful sense, but as it was it was purchased with obscene amounts of luck and the active collaboration of the Federal officer who was charged with commanding the Army of the Potomac (one cannot really call McClellan a "commander").
Gettysburg is at the same time both similar and different. Lee's plan for that campaign was basically to throw **** at the wall and see what stuck. (This was as advanced as Confederate offensive operational planning got.) At least theoretically, he recognized the potential for fighting a "decisive battle" on northern soil and winning. Whether that would involve an advance on the capital afterwards was unclear, but it was at least potentially, theoretically, in the realm of possibility. But if attacking Washington was at least possible in Lee's mind, it's hard to see how it would have been possible in terms of the actual campaign. If the ANV were chased by the Army of the Potomac, it would march to concentration, unite, and destroy it (although this is overstating the effect of
calculation on the decision to fight at Gettysburg, which was made out of a vague sense that it was a good idea as much as if not more than an actual CBI or plan of campaign).
But that "destroy" part is tricky. Until the Appomattox campaign, no field army on either side of the war was ever really "destroyed". Lee, Grant, and Hood all came reasonably close: Lee's ANV disintegrated a large portion of the Army of Virginia at Second Manassas and induced the War Department to disestablish the army and parcel out its troops among other units. Grant forced Pemberton's army at Vicksburg to surrender, although it wasn't really a full field army and he ultimately ended up paroling most of it. And Hood annihilated his own Army of Tennessee in the battles of Franklin and Nashville, although again enough of it remained to significantly bolster Joe Johnston's extemporized force that tried to bar Sherman's way through the Carolinas in early 1865. So ignoring all of the tactical and operational problems that made a Confederate victory at Gettysburg extremely unlikely - and there were zillions of them -
even if the Army of Northern Virginia somehow won the battle, it would not have destroyed the Army of the Potomac. Meade's army would still exist. Perhaps it would still be almost completely intact, and give battle again at Pipe Creek, another opportunity for Lee to lose depressingly large numbers of soldiers.
Or perhaps it would be badly mauled, and retreat into the fortifications of Washington. What would happen then? Think about how difficult it was for the Army of the Potomac, the Army of the James, and the Army of the Shenandoah to smash the Confederate defenses of Richmond and Petersburg in 1864 and 1865, despite possessing a vastly numerically superior force that was much better armed and equipped, commanded by one of the best officer corps the United States military has ever turned out. Now think of how incalculably more difficult it would be for the Army of Northern Virginia to do the same to Washington - possessing inferior numbers, arguably inferior quality in generalship and the average soldier, fewer munitions, and confronted by a system of forts that put the extemporized field fortifications of Richmond and Petersburg to shame. Lee could no more break this ring and lead a triumphal review down Pennsylvania Avenue than conquer the Moon for slavery and the planter class.
