The reason the States seceded was States Rights and the Morill Tax.
Like Democratic politicians of this very day and age, the issue was brought to false importance by Lincoln as a way to gain support for his over-the-top, slash and burn, scorched earth policy against American citizens who were fairly exercising their Constitutional rights. Lincoln stated the reason he could not allow secession was that the government simply could not survive on its own resources in the North. “The Great Emancipator” only became inured of the defense of freeing the slaves as a political ploy.
Here are some of Lincoln’s comments on African-Americans before it became politically expedient for him to change them.
Abraham Lincoln Quote
“I will say then that I am not, nor ever have been in favor of bringing about in anyway the social and political equality of the white and black races - that I am not nor ever have been in favor of making voters or jurors of negroes, nor of qualifying them to hold office, nor to intermarry with white people; and I will say in addition to this that there is a physical difference between the white and black races which I believe will forever forbid the two races living together on terms of social and political equality. And inasmuch as they cannot so live, while they do remain together there must be the position of superior and inferior, and I as much as any other man am in favor of having the superior position assigned to the white race. I say upon this occasion I do not perceive that because the white man is to have the superior position the negro should be denied everything.”
African-Americans have been allowing themselves to be bought and sold by politicians ever since.
http://www.ashevilletribune.com/archives/censored-truths/Morrill%20Tariff.html
Gee, if only they'd actually mentioned the Morrill Tariff in their Declarations of Causes instead of constantly going on about slavery and the threat to it presented by the election of Lincoln, you might have a point.