[Cyrien]

The south worked on credit. If you look at the figures the south (later just before the civil war) imported large portions of their food from the north and manufactured goods.

To use a modern term the south was a bannana republic. They produced and sold cotton as an agriculture product and exported it to foreign markets. Most of it was sent to be processed into fabrics etc either in the north or most of it in England.

The economic collapse of the south was largely due not to the north or the loss of slavery but to the production of high quality cottons in Egypt and India by the British Empire which had been the largest buyer of southern cotton.

Regardless of the civil war or slavery etc the southern economy was on the very edge of collapse anyways, the above two just hastened it. In fact you can track the cost of cotton globally for the time period and see it decline as the English began production of it in their colonial holdings. They filled their own majority demand and that of many others at lower costs.

The southern economy was as efficient as any modern nation that specializes in a single export cash crop. The advantage the south had over todays modern nations was the fact that they weren't a nation specializing in it but rather half of a nation specializing while the other half was diversified (until the Civil War, then you can look at how efficient their single line economy was against the diversified economy of the north despite the south having the better military tradition and military commanders.)