That is simply not true. All 11 confederate states and 2 rump conventions in border states published what they called "Ordinances of Secession." Not one of them mentions a thing about slavery beyond a geographical reference.
In addition to the 11 Ordinances, which every confederate state published, the membership of the conventions of four states (Texas, Georgia, Mississippi, South Carolina) drafted legislative resolutions listing certain causes. These four documents were very heavily pro-slavery, but not entirely devoted to the issue. The tariff issue was listed briefly in the Texas legislative resolution. Georgia's legislators talked about the tariff issue at length in multiple paragraphs.
That's not true.
The Mississippi secession convention began their declaration of causes with the statement, "Our cause is thoroughly identified with the institution of African slavery."
"And Texas:
...[the Northern States] have united in the election of a man to high office of the President of the United States, whose opinions and purpose are hostile to slavery. He is to be entrusted with the administration of the common Government, because he has declared that the `Government cannot endure permanently half slave, half free,' and that the public mind must rest in the belief that slavery is in the course of ultimate extinction."
"They demand the abolition of negro slavery throughout the confederacy, the recognition of political equality between the white and negro races, and avow their determination to press on their crusade against us, so long as a negro slave remains in these States."
--Texas Declaration of Secession.
And South Carolina:
"For many years these laws were executed. But an increasing hostility on the part of the non-slaveholding States to the institution of slavery, has led to a disregard of their obligations, and the laws of the General Government have ceased to effect the objects of the Constitution."
http://members.aol.com/jfepperson/plat.html
GOPCap is peddling more manure. But the record is plain.
Walt