The economics of slavery is of course a highly debatable issue. I tend to think that it was a growing and profitable arrangment prior to the Civil War. A book named: "Time on the Cross" provides some supporting evidence. Here are some of the book's conclusions:
1. Slavery was not a system irrationally kept in existence by owners who failed to perceive or were indifferent to their best economic interests. The purchase of a slave was generally a highly profitable investment which yielded rates of return that compared favorably with the most outstanding investment opportunities in manufacturing.
2. The slave system was not economically moribund on the eve of the Civil War. There is no evidence that economic forces alone would have soon brought slavery to an end without the necessity of a war or other form of political intervention. Quite the contrary; as the Civil War approached, slavery as an economic system was never stronger and the trend was toward even further entrenchment.
3. Slaveowners were not becoming pessimistic about the future of their system during the decade that preceded the Civil War. The rise of the secessionist movement coincided with a wave of optimism. On the eve of the Civil War, slaveholders anticipated an era of unprecedented prosperity.
4. Slave agriculture was not inefficient compared with free agriculture. Economies of large-scale operation, effective management, and intensive utilization of labor and capital made southern slave agriculture 35 percent more efficient than the northern system of family farming.
5. The typical slave field hand was not lazy, inept, and unproductive. On average he was harder-working and more efficient than his white counterpart.
6. The course of slavery in the cities does not prove that slavery was incompatible with an industrial system or that slaves were unable to cope with an industrial regimen. Slaves employed in industry compared favorably with free workers in diligence and efficiency. Far from declining, the demand for slaves was actually increasing more rapidly in urban areas than in the countryside.
7. The belief that slave-breeding, sexual exploitation, and promiscuity destroyed the black family is a myth. The family was the basic unit of social organization under slavery. It was to the economic interest of planters to encourage the stability of slave families and most of them did so. Most slave sales were either of whole families or of individuals who were at an age when it would have been normal for them to have left the family.
8. The material (not psychological) conditions of the lives of slaves compared favorably with those of free industrial workers. This is not to say that they were good by modern standards. It merely emphasizes the hard lot of all workers, free or slave, during the first half of the nineteenth century.
9. Slaves were exploited in the sense that part of the income which they produced was expropriated by their owners. However, the rate of expropriation was much lower than has generally been presumed. Over the course of his lifetime, the typical slave field hand received about 90 percent of the income he produced.
10. Far from stagnating, the economy of the antebellum South grew quite rapidly. Between 1840 and 1860, per capita income increased more rapidly in the south than in the rest of the nation. By 1860 the south attained a level of per capita income which was high by the standards of the time. Indeed, a country as advanced as Italy did not achieve the same level of per capita income until the eve of World War II.
Several of these, such as the matter of the profitability and viability of slavery or the growth of demand for slaves in cities, were already well-known conclusions at the time and were the product of other researchers (Conrad and Meyer, Stampp, Yasuba, and Goldin, among others). Fogel and Engerman may have added a bit to these sorts of issues, but their role was more that of making such results more widely known among the general public and integrating that information into their bold, new vision of the way the slave system functioned.
Other revisionist claims were provocative. Could slave agriculture possibly be more efficient than free? Was the family the basic unit of social organization under slavery? Was the material condition of slaves as favorable as that of free industrial workers? Was the rate of exploitation or expropriation really that small? Did southern per capita income increase faster than that in the rest of the nation? The slave-based, monocultural agricultural system of the South was Douglass North's archetypal example of an economy that was not going to be successful. Did he get it all wrong?