The main advantages that the South held during the civil war were the vast ranks of experienced generals and soldiers, along with the benefit of being able to maintain defensive positions. While the North had far more resources and population, in order to unite the country, President Abraham Lincoln had to take the offensive to defeat the Southern rebellion.
The South was better prepared for battle than the North, mainly due to the Mexican-American war. Soldiers were more experienced and knowledgeable, and nearly all of the best tactical minds in the country were contained within the Southern states. Comparatively, the North struggled to find competent leadership for its military.