Popular opinion in the North and the South held that the war would be short and relatively bloodless. Northerners thought southerners would quickly capitulate when faced with overwhelming force, and southerners thought the North lacked the resolve to fight against southerners, who they thought were inherently better fighters. In both regions, calls for enlistment were (for about the only time in the conflict) answered enthusiastically.
The major differences between the two regions were material. The vast majority of industry in the United States was in states that had not left the Union, and the Southern economy was based largely on cash crop agriculture, which they hoped to use to leverage European support for the Confederacy. The North also had a much larger population than the South, and it is important to remember that a very significant portion of the South's population of military-aged males were slaves, and the Confederacy refused to arm them. The North also had an enormous infrastructural advantage, with many more miles of railroad.