Absolutely. It produced 200 million per year (funneled through New York) and was making money for both sides. That's why it was valued at 4 billion. If it weren't producing the money, it wouldn't be worth anything to the people who ran those economies back then.
But look there. You created another opportunity to say the word "slave" while dripping it with the appropriate level of disgust. Once more you have reminded us how very very very much you hate slavery. Good Job!
The Milk of human kindness was not motivating either the Southerners or the Northerners at this point in history. It was all about the money.
So then Southerners DID secede to preserve slavery, since that was the source of their money. That’s the inescapable conclusion to be drawn from your own words.