The North had a heavily industrialized economy while the South's economy was still mainly cash crop exports such as cotton. So when the Civil War broke out the North already had the means of production and the production capacity to make arms and supplies for their troops as well as deliver the supplies to the troops in a speedy manner via the North's extensive railways. Now the South basically had to build its production facility for its war efforts because it had an almost non-existent industrial capacity making it severely lag behind the North in its abiity to supply its troops. Also before the Civil War broke out the US had a lot of pro-industrial tariffs in place which made the Northern states generally wealthier the the Southern states.
