South Carolina's Declaration of Secession says the preservation of slavery was the main reason for secession. The rest of the CSA joined them in that effort.
You keep saying this, but the declarations of four states (found at the link here: http://sunsite.utk.edu/civil-war/reasons.html#South%20Carolina) state that they seceded in defense of self-determination and to protect themselves from radical northern anti-slavery. There is a difference. Northern radicals felt their moral position gave them the power to violate the constitution with impunity. Before you jump in and agree with them, remember that abortion clinic bomber Robert Eric Rudolph feels the same way. So does Osama bin Laden.
Respectfully,
D J White