“The South had the upper hand and the momentum up until this point. They were fighting in Northern territory!” And in so doing lost many of the tactical advantages that the ANV enjoyed when fighting on their home turf. The failures of JEB Stuarts cavalry division to properly screen the advance could not be compensated for with local friendly intel.
JEB Stuart screwed up BIG TIME at Gettysburg. Lee lost confidence in him after that.
The absence of Stuart’s cavalry immediately before the Gettysburg fight, when Lee had been depending on Stuart’s cavalry to act as his eyes and ears, put Lee into an almost impossible position, and left him only two real choices: Attack with what he had and with what he knew; or withdraw. For several reasons, Lee could not withdraw. Thus, he found himself having to attack; and at that he almost won the fight.
The south had won defensive battles in the east, but lost in the west. Tennessee was lost, along with the south’s major source of pork (protein). Vicksburg chopped off Texas (beef), Arkansas, and took most of Mississippi. After defeat at Vicksburg, US forces would turn east toward Chattanooga and Atlanta’s capture would assure the reelection of Lincoln.
The south was losing the war, but just losing more slowly in the east due to the decision to suck more rebel units from the west to the east.
And as the south slowly lost in the east, US Naval supremacy on the high seas took increasing effect.
The strategic reason for moving into the North....
Vicksburg was taking a beating with the siege and so the thought was to counter the Vicksburg move with an “invasion” of the North. It was intended to strike fear into the Northerners.
The turning point was Picket's charge. The commanders lost their nerve and fell back to an old failed strategy of moving their troops in a massive formation towards an objective. I think it is referred to as Napoleonic tactics. Technology had made it obsolete. Besides, Lee was best suited for gorilla tactics versus direct face to face attacks.