The full preamble of the Mississippi declaration is fascinating, and further shuts down doubters that the civil war wasn't about slavery and racism:

> 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

Also, they clearly make the case that cotton was the most important good in the world, perhaps imploring the intercession of foreign powers.

I think it's worth pointing out though that these people were not being honest with themselves - nothing in their argument about the importance of cotton suggests it couldn't have been done with wage labor. They are dancing around the fact that only a very few benefit from slavery.