Mississippi seceded from the union on January 9, 1861, by a vote of 84 to 15 at a convention in the state capital in Jackson. To explain its decision, the delegates issued a "A Declaration of the Immediate Causes which Induce and Justify the Secession of the State of Mississippi from the Federal Union," which begins:
In the momentous step which our State has taken of dissolving its connection with the government of which we so long formed a part, it is but just that we should declare the prominent reasons which have induced our course.
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.
Read the rest: http://avalon.law.yale.edu/19th_century/csa_missec.asp
Top and above, Civil War statue in Cleveland, MS