There are many reasons why the South lost the Civil War, but none more than population. The north had 22 million people while the south had only 5 ½ million. The south mobilized 70% of their manpower. The south also lost about half that population to death and permanent injury. By the end of the war, whenever a southern soldier died there was a hole in the line. When a northern soldier died there were four more men behind him to take his place. With the differences it is almost a better question to ask how the south fought for as long as they did.
Historically Speaking 