Further, if you want to take "their" words at face value, read Georgia' articles of secession. It goes into a long historical explanation of the roots of the problem.
Georgia was clear that the preservation of slavery, but more importantly the extension of slavery and the possible addition of slave states was important to it and the reason it was seceding. Georgia's wealth, like most of the wealth of the South was tied to slavery and it could not get out of the trap easily.
However, Georgia traced the roots of the crisis in 1860 to tariffs and government subsidies for Northern manufacturing and trading interests. These interests had always gotten what they wanted until the South and the North West stood up to them and finally settled the issue in 1846. There would be no more mercantilism and subsidies for those industries. IT WAS THEN AND ONLY THEN, that these interests threw their money behind the still relatively small abolitionist movement in order to break the power of the South and thus, take control of the government.
Those manufacturing and trade interests knew that if they could break the power of the South, the federal government would pour money into them hand over fists. And if you look at it, that is exactly what happened. Before the Civil War was even over, the biggest government subsidized boondoggle in our history started with the funding of the multiple transcontinental railroads. Sure, they were a boon to commerce, but the graft and corruption in their building has never been equaled. They were making millions per mile in federal funds.
Those pursuits would have had to be privately funded had the South retained its pre-war position in the Union.
