Answer:
Negative, but not by much.
Step-by-step explanation:
During the civil war both Northern and Southern states in USA had to pay a lot of expenditures for the military's wages , equipment's, and supplies. On top of that, it caused the loss of a lot of labor forces in north and Sothern states.
But after the civil war was won, the southern states no longer able to use slaves. So, the plantations start using technologies from the industrial revolution that make the production actually become more efficient. This almost made up for the lost that incurred from the war in term of GDP.