Answer: D. Superior generals
Explanation: During the Civil War, the North had the advantage in almost all aspects necessary for a military campaign. But in addition, an important factor was moral, which, at least at the beginning of the war, was on the South side, since they were those who defended themselves, and knew the good terrain in which the battles were taking place. Thus, the number of soldiers in the first year of war was the same on both sides, although the number of southern states in the war was far smaller. South also proved to be resourceful in improvising production for the needs of the war. Although, the greater economic power of the North and the greater number of people, especially in the later years of the war, proved to be decisive.
What was certainly exclusively the advantage of the South were superior generals, given that the vast majority of military academies were in the South, giving outstanding military strategists and tactics.