Well yeah, with the North keeping most of the 750 million dollars per year the South pumped into their economy, the South always was at an economic disadvantage, but it had nothing to do with the "free market."
Washington DC was *FORCING* the South to pay 72% of all the taxes, and *FORCING* them to hire Northeastern companies to handle all their shipping, banking, warehousing, financing, insurance and other needs, which is how so much Southern money kept getting pumped into the Northeaster economy.
This isn't a "Free market". It is closer to fascism.
The Slavery System was a failure, semi ,- Socialistic and inherently anti- free market. Leading Southerners actually referred to the Slave Economy as Socialist. The US Government was small before before the war.