The question was recently asked, of a large number of notable American Civil War historians, what would have changed if Stonewall Jackson had been at Gettysburg?
The general consensus was that Jackson would not have changed much, or that the way in which his presence would have changed things is not the one most commonly assumed. A major what-if in the Gettysburg historiography has been the question of what would have changed on the first night if Jackson had been present. As several of the respondents noted, Richard Ewell, the man with the unfortunate task of replacing Jackson, did a fine job on the first day of Gettysburg. He is often condemned for failing to take Cemetery Hill on the first day of Gettysburg, but the bulk of the relevant sources and scholarship is firmly on his side; with what he had available, and Lee’s ambivalence towards further action denying him reinforcements, he simply could not have taken the hill and smashed the Union army on the evening of July 1. At most, Jackson’s presence could theoretically have resulted in Confederate occupation of Culp’s Hill, a lightly defended position on the Union right that if taken, could render Cemetery Hill untenable. In the event of that happening however, the Battle of Gettysburg would have become a one-day prelude to a battle along Meade’s planned defensive line further south, at Pipe Creek.
Much more could be said about the potential possibilities of Jackson at Gettysburg, of course. Some of the respondents were also thinking about Jackson on the second day of Gettysburg. The bottom line however, is that despite the loss of Jackson and the reorganization that entailed, the Gettysburg Campaign was not lost because of the changes within the Army of Northern Virginia. The Gettysburg Campaign was won because of the improvement of the Army of the Potomac under Joseph Hooker and the rise to command of George Meade. Under Meade, the Army of the Potomac, fighting on its own soil, was united in purpose under a commander who wouldn’t be intimidated or panicked for the first time. Against a larger, well-trained army, clearly superior in artillery, fighting a defensive battle, and for the first time without prohibitive leadership holding it back on the field, it is unlikely in any eventuality that Lee could have decisively overwhelmed the full force of the Army of the Potomac in the field, with or without Jackson. As George Pickett reportedly said when asked why the Army of Northern Virginia was defeated at Gettysburg, “I always thought the Yankees had something to do with it.”