I have to agree with the original poster, I mean it's not like the first state to succeed, South Carolina, ever mentioned slavery. Not even as a reason to succeed in the first paragraph in their succesion document - hmmm what's this over at
http://avalon.law.yale.edu/19th_century/csa_scarsec.asp? Why it's South Carolinas very own succession document! Hmmm, I wonder what the very first paragraph says...
The people of the State of South Carolina, in Convention assembled, on the 26th day of April, A.D., 1852, declared that the frequent violations of the Constitution of the United States, by the Federal Government, and its encroachments upon the reserved rights of the States, fully justified this State in then withdrawing from the Federal Union; but in deference to the opinions and wishes of the other slaveholding States, she forbore at that time to exercise this right. Since that time, these encroachments have continued to increase, and further forbearance ceases to be a virtue.
What're those last few sentences? Ehh probably nothing.