The North had international legitimacy. Other nations recognized the North and could provide trade and credit. The Confederacy, on the other hand, never received international recognition. While Britain unofficially built commerce raiders for the South, the states in rebellion could not rely on international aid.
The North had more fighting men than the South. Eventually this would come to bear in terms of both supplying men to fight as well as men to provide supplies and food to the armies. The South could not afford a long war of attrition. The quality of troops in the North increased as the war progressed, while the South was taking the young and the old to fill its ranks before the war was over.
The North had greater infrastructure. Railroads allowed the North to ship men and supplies where they were needed most. Lee's final retreat to Appomattox was plagued by a poorly organized rail service. Even before the war, the South lacked railroad investment.
The North also had a moral reason...
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