That is really the problem with the way the NPS and many Northerners portray the reasons for the war. To ennoble their version, they insist the war was fought over slavery and those few apologists among them that realize that this is a twist of the facts, insist at the very least, that slavery was the underlying issue for the war. This is true in that, slavery was protected by the US Constitution and the real issue was that the Abolitionists were trying to undermine the US Constitution!

The Southern States that seceded from the Union were merely attempting to ensure the rights guaranteed by the Constitution. With the election of Lincoln and many Radical Republicans, they no longer believed that their rights would be protected, hence secession. It wasn't long before the Lincoln administration lived up to their advanced billing and started to circumvent provisions of the Constitution.

However, Lincoln and the Radical Republicans that came to the fore by the end of the war, won the war. Is it really any surprise that their view of the history of the war (ie. fought to free the slaves) has become the predominate view of mainstream academia? It's vital that the war remains an important event in the lives of the Southern people, because that is the only way that some historical balance can be achieved.