The northern part of the U.S. did not launch a rebellion to protect slavery. The Southern states did.
You repeatedly keep dragging up the word "slavery" to justify what your side did, and you keep ignoring the evidence that they didn't really do what you are claiming.
All the justification the U.S. needed was the fact that the Southern states claimed to have left and then launched a war to further their aims. The U.S. goal in fighting the war that was forced on them was first, last, and always to preserve the Union. Slavery didn't enter into the motivation, and the fact that the institution was fatally weakened during the course of the war and was finally done away with shortly after it ended was one of the few happy outcomes of that tragic and bloody conflict.
So lets say they launched a rebellion to protect their forest timber. Would that allow them to exercise their rights to leave?
You keep holding up that "slavery" shield to protect yourself from having to defend a clearly tyrannical position.