I think that the CSA was legitimately a country. The USA is meant to be ruled by the people, and when that many people are displeased with the government it should be the government's place to do something about it. If the North had recognized the unhappiness in the South and done something about it, then there wouldn't have been an issue. They declared independence from a government that they didn't feel was doing what they wanted it to do. The only problem was that the old government failed to recognize it's failures and let its displeased citizens go and just try and do better in the future. The USA tried to hold onto post offices, governemnt land, and forts. If they had let all land in the new country go and stopped trying to occupy land that they no longer owned, then we could have just had two American nations. But of course they couldn't let that happen. They had to try and maintain a militaristic presence in a country they had the chance to reconcile with but refused to do so. I'm not saying that the Civil War was a war of Northern Aggresion, but they had plenty of chances to avoid it.
I'm not one of the "South will rise again against the vile Northern oppressors" type of people, but I do think that both sides are equally at fault and that states should have some rights, including the right to leave the federal government if they feel that it is not fufilling it's duty or if the majority of the population no longer wishes to be with the federal government, which was the case in the 1860's.