A few more points, for what ever they may be worth.
It is a mistake to see the Gettysburg Campaign as an attempt to occupy Southeastern Pennsylvania, Baltimore or Washington. The campaign was a huge raid designed (at least according to Lee’s explanation to Jeff Davis after Chancellorsville) to get the Army of Potomac out of Virginia so that a crop could be harvested to feed the Southern Army the following winter, to force the North to pull troops out of the Western Theater to deal with Lee and thereby relieve Vicksburg, and to catch the Army of the Potomac at a disadvantage and fight a decisive battle. Lee succeeded in his first objective—the Army of the Potomac did no significant campaigning in Virginia until the next spring when Grant initiated his overland campaign starting with the Battle of the Wilderness. In the other two objectives Lee failed. The campaign did not relieve the siege of Vicksburg or lead to a decisive Union defeat.
The Confederate attack on the second day, as conceived by Lee, assumed that the Union left flank lay on the south edge of Cemetery Hill and was intended to sweep up the Emmetsburg Road to hit the supposed exposed Union flank. When Longstreet tried to place McLaw’s Division pointed East toward the Round Tops Lee forcefully corrected the disposition so that McLaw’s Division advanced to the Northeast with its left flank on the Emmetsburg Road. In fact, the Union Second Corps had taken position along Cemetery Ridge from the cemetery to the South and the Union Third Corps had taken up position extending the Second Corps line to the South to the Round Tops. An attack up the Emmetsburg Road would have exposed its right flank to savaging by Union artillery along the ridge and to attack in flank and rear by the infantry. It was only the unauthorized advance by the Union Third Corps to the Peach Orchard position that saved Lee’s plan.
By the end of June, 1863, Lee had no incoming supply line from the South. There was an outgoing supply line sending horses, cattle and grain , and, most reprehensively, Black residents of Northern Maryland and Southern Pennsylvania, from the Chambersburg, PA., area south to the Valley of Virginia, but Lee was drawing no supplies from Virginia. Lee’s army was living off the land. That worked as long as the army could spread out and send out foraging parties. It did not work when the army was concentrated for an engagement. Once concentrated, without a regular source of supply, Lee’s army could not stay in one place more than a few days.
While Lee was able to forage beef, pork, corn and wheat form the country side, no amount of foraging would produce ammunition. By the third day of the battle the Army of Northern Virginia’s supply of artillery ammunition was just about exhausted. Lee had no place to secure a resupply of ammunition this side of Staunton, Virginia. Lee certainly did not have enough artillery ammunition with his army for a fourth day of fighting. Lee’s inability to feed his army for more that a few days and the shortage of ammunition, along with the high confidence inspired by the Battle of Chancellorsville, had much to do with Lee’s decision to adopt a measure as desperate as Picket’s Charge.
In order to get France, and more importantly England, to intervene in the Civil War the Confederacy had to prove to the European Powers that it would win the war and secure its independence and that Europe needed the South. To do that Lee had to destroy a major Union army as the Colonial Rebels had destroyed Burgoyne’s army at Saratoga in 1777, and as Grant was about to do to Pemberton’s army at Vicksburg. It was not enough that the Confederacy demonstrate an ability to resist Union conquest. The European Powers were willing to bet only on a sure thing. Without the destruction of the Army of the Potomac as a fighting force there was no sure thing. France (read Napoleon III) had adventurous tendencies and had invaded Mexico and was willing, even eager, to secure Southern independence and protect its Mexican empire by getting into the Civil War but was unwilling to do so without English support. The South did not help its case any when it chose to prove to England just how important it was by embargoing its own cotton shipments to the English mills. Egyptian cotton and Indian cotton made up the difference after a period of hardship in the fabric trade. In the face of this England concluded that it did not need King Cotton. This left England with the opportunity to slap a rival as its only real motivation to work for Southern independence. This motivation was largely countered by English abhorrence of slavery. Absent a decisive Confederate victory England and France were not jumping into the war.
