Here are some excellent articles (from a black writer) on the legality of secession:
http://walterewilliams.com/secession-or-nullification/
http://www.newsbusters.org/blogs/nb/walter-e-williams/2012/12/03/walter-e-williams-column-secession-craze-isnt-crazy-parting
http://www.wnd.com/2012/11/secession-its-constitutional/
http://walterewilliams.com/the-real-lincoln/
Doesn’t matter what the academics decide or say now. A war was fought.