There is a point that Bill Moyers makes in his book on Democracy. The Civil War was a major point in the definition of citizenship. A large part of the reason many of the Southern generals elected to serve the Confederacy is that, while they were generals in the American army, they still considered themselves Virginians, Kentuckians, etc. first. Lee struggled with this before going South. He was offered command of the Union army but decided he could not fight against his home state.
Although condemned as traitors, these people were being true to what they considered their true citizenship. The war helped redefine the definition of American citizenship.