Georgia and Mississippi specifically stated slavery, or, the freeing of slaves and confiscations of slaves, as examples of federal overreach. Mississippi also further clarified, pretty much equating it to a modern day economic sanction.
From the Mississippi articles of secession:
"Our position is thoroughly identified with the institution of slavery - the greatest material interest of the world. Its labor supplies the product, which constitutes by far the largest and most important portions of commerce of the earth. These products are peculiar to the climate verging on the tropical regions, and by an imperious law of nature, none but the black race can bear exposure to the tropical sun. These products have become necessities of the world, and a blow at slavery is a blow at commerce and civilization. That blow has been long aimed at the institution, and was at the point of reaching its consummation. There was no choice left us but submission to the mandates of abolition, or a dissolution of the Union, whose principles had been subverted to work out our ruin. "
The rest of the states who seceded cited simple federal overreach, and federal government basically not doing their job (to put it very
simply), except for two.
Those two being Missouri and Kentucky. Their articles of secessions state that they wanted to secede because war was waged upon them against their will by the federal government. Basically, "I wanted no part of this mess, but you started it!!"
Oh, I wouldn't think of not citing a source...
So... in my mind... 1 state using the freeing of slaves as an example of federal overreach, and another state actually pretty much citing slavery as nearly the sole purpose (sometimes I'm not so proud of my home state...), hardly makes the issue solely that of slavery.
Was it an issue, before, during, and after? Yep. Was it THE
issue? In my home state of Mississippi, and even then, it was basically the fear of absolute financial ruin without slave labor. The rest wanted the states' rights that was promised to them.