The following is part of a longer essay which appeared on Daily Kos. It was written by Joan Jacobsen who is a Civil War historian.
Because of hurt feelings in the South, because of the “Lost Cause”-myth and because of the general American adulation of anything or anyone wearing a uniform … a cultural trait which honestly confounds and bewilders many non-Americans … the Confederate soldiers and leaders are considered heroes to this day. Great men who fought valiantly for a “Lost Cause”.
But it is a lie.
They were traitors to their nation. There is no other term that applies. I realize that they felt differently, and that for example Robert E. Lee felt saddened by the rebellion, while at the same time feeling that Virginia was his "country" and that he couldn't take up arms against it. But Virginia was not an independent country, nor was any other state. I find it difficult to believe that highly educated men like the Confederate leaders generally were, did not know the difference between a confederation of independent nations and a federation of states. The issue of "states rights" did not make each state an independent, autonomous nation. States rights simply gave each state a certain level of autonomy on some issues. Today, we'd call that kind of thing "home rule" and it is still in use in various parts of the world. It gives certain areas or territories, such as Greenland, which is formally a part of Denmark, the right to self-determination on certain internal affairs, although they are still subject to being overruled by the parliaments of the "mother country". The same thing went for the rebel states in 1861. They could make decisions on internal affairs, subject to being overruled by the federal government.
This included the issue of slavery. While ostensibly an internal affair, a federal emancipation of the slaves would have overruled the legislation of the individual states.
This was not only known to the state assemblies in the rebel states. It was precisely the reason why they seceded. Ergo, they acknowledged that states rights were superceded by federal legislation. It was never, as later Confederate apologists would have us believe, a matter of the federal government overreaching. The precise and exact reason why the rebel states seceded was because they knew they were subordinate to the federal government, and they wouldn't accept it.
That makes their act of secession treason by definition.
Please read the entire article here.