There are many answers to this question but perhaps the most logical answer is that it ended the ability of the Confederate Army of Northern Virgina to sustain offensive actions. From Gettysburg...
The single most important strategy was to block the Confederate Army from attacking or surrounding Washington. The strategy developed over 4 days to include taking fixed, fortified positions they...
Neigther the north or the south gained anything in this battle. However, it stopped Robert E. Lee from moving on an winning this battle (he surrendered). It is also the battle where you could say...