And what was the reason that the South was such an economic powerhouse? Oh, that's right, it was SLAVERY; it was the fact that they had an almost unlimited source of nearly free labour, something no other country who did not engage in the slave trade had. And the primary cost of production at that time was... let's see... oh right, it was labour.
The Confederacy was a collection of states whose economies were based on slavery. Trying to frame this as an economic conflict completely ignores the fact that the entire foundation of the South's economy was chattel slavery. That is why the South fought so hard to keep slavery, and why nearly all of the Confederate states articles of secession explicitly stated that slavery was the reason they (unlawfully) seceded. Recognizing the humanity and equal rights of slaves destroyed the entire basis for their boom economy; they had a huge vested interest in maintaining the sub-human status of their chattel.
And it's not like it was an economic benefit to all the non-slaves of the southern states. Much like the modern situation, the vast majority of the wealth in the south was sequestered in the hands of a very small number of elites who were wealthy enough to own large plantations, and the slaves needed to work those plantations. It was these elites who formed much of the government of the Southern states, and pandering to them was the reason for the secession; which was not done with a popular vote, but a unilateral declaration by bought-and-paid-for politicians.