Why did the American Civil War drag on for 4 years?

One of the main problems of the protracted nature of the Civil War was that the United States underestimated the South. At that time, the Confederates had a better army, especially its commanding staff. This allowed them to achieve victories in battles even with the numerical superiority of the enemy. Thus, the war dragged on. However, the gradual numerical superiority of the North, as well as the naval blockade of the South, turned the balance to the side of the United States. Ultimately, the war ended in victory for the northern states.