I’ve written at great length about the constitutional issues involved in the Civil War, mostly in response to the increasingly popular argument that secession actually was constitutional and that the Lincoln Administration had no legal authority to use force against the Confederacy—but also in response to various other criticisms of Lincoln and the Union cause. My most thorough discussion of these issues is my article, How Libertarians Ought to Think About The U.S. Civil War, but I also have been blogging about this at my personal blog, Freespace. You can read part 1 here, part 2 here, and the succeeding parts as they appear in the coming days.
Also, these posts from some years ago are still relevant:
1. Sovereignty, Lincoln, Sense and Nonsense
2. The South Shall Rise Embrace Hypocrisy And Logical Fallacies Again!