This left the Confederacy with two options. Lee could fall back to the defenses around Richmond and send a large portion of his army to try to help Vicksburg, or he could embark on another invasion of the North. He chose the latter, and went to Richmond 150 years ago today for a multi-day conference with high ranking Confederates.
It was hoped that an invasion would accomplish a few purposes. First, it would demoralize the northern populace, and it might convince the government in Washington to pull troops from Vicksburg to meet Lee's threat. Second, the food supply in Virginia was diminishing, and it was getting harder and harder to find supplies in the places through which the armies and marched and counter marched. Moving north he could live off the enemy's country. And third, always in the back of Lee's mind was the thought that if he gained a great victory on the Union's own ground, he might finally be able to follow up on his victory, capture Washington, and perhaps even end the war. Lee believed continued defeats would mean that Lincoln would loose the election next November, and if Lincoln lost the election doubtless the war would end. He wrote to his wife:
If we can baffle them in their various designs this year, next fall there will be a great change in public opinion at the North. The Republicans will be destroyed & I think the friends of peace will become so strong as that the next administration will go in on that basis. We have only therefore to resist manfully ... [and] our success will be certain.It was for all these reasons that Lee decided, with the agreement of the government in Richmond, to attempt another invasion of the north.