Actually he's asking the question from the Confederate point of view. What were the Confederates goal in waging their war? To defend slavery. I would have thought that was obvious.
Whether he is asking the question from the Confederate's point of view is irrelevant. They did not have control over the prosecution of the war. It is not their choice to keep the war going, it was the Union reasons that kept the war going.
Once again I point out to you, that if "slavery" was the reason and the only reason why the confederates fought, then why didn't they simply rejoin the Union? Lincoln was saying they could keep their slavery, and they had it before Lincoln became President, so why would they fight for something which the other side was willing to give them?
Again, why would they need to fight for something which the other side was willing to give them?
The facts simply do not support the contention that either side was fighting over slavery, because slavery was not being threatened by the war. (at first.)
What was being threatened by the war was Independence. That was the non negotiable. Slavery was an acceptable compromise for the Union, an Independent South was not.