The centuries-old debate over the profitability of slavery has flared again, prompted by a recent article in The Economist.

It's a debate that has been discussed in academic circles for more than 150 years, with one of the most notable evaluations done by economist Thomas Gowan in 1942. Gowan concluded that plantation slavery was indeed most often profitable to the larger class of slave owners, despite his efforts to prove it was not, and many economists have supported Gowan’s theory over the years, with little evidence to suggest otherwise forthcoming.

Robert Fogel and Stanley Engerman wrote in their 1974 book, "Time on the Cross: The Economics of American Negro Slavery," that slavery was perhaps more profitable than other investment opportunities in similar industries, such as farming. Slavery was “generally a highly profitable investment that yielded rates of return that compared favorably with the most outstanding investment opportunities in manufacturing,” they wrote.

Instinctively it would make sense that free labor would bring more profits than paid labor, but many authors on the subject suggest that slavery was not as lucrative as has been thought.

Irishman John Elliott Cairnes, often referred to as the last great classical economist, believed that slavery had an overall negative impact on the economy of the South in 19th century America. His basic argument was that reluctant workers had no interest in learning new farming techniques and therefore weakened soils much quicker because they didn’t have the basic requisites for farming.

This meant that the South was less competitive than the North, where free slaves were being paid to learn and maintain farms to a better standard, thus growing more and better crops.

There is also a school of thought, written about by Ralph Anderson and Robert Gallman in the Journal of Ameican History in 1977, that suggests the South found it difficult to establish trading networks because the skill base of its slaves dictated what crops they were able to grow effectively. And in the case of bumper crops or weak demand, planters would suffer big losses.

The free states in the North not only were able to recruit the relevant employees for the correct season, they could also train the workers to adapt. Slaves in the Southern states were long-term investments and in that respect, did not have the flexibility that the open employment market of the North did.

Perhaps the most tenuous of all claims was the sociological theory of Eugene Genovese, who in 1961 claimed that the antebellum Southern planters were not out to make profits but rather to flaunt their huge plantations and large numbers of slaves.

The modern thinking that slavery was not profitable appears to make more sense, and it was perhaps this that led to its demise.

Nobel Prize-winning economist Douglass North, a professor at the University of California, writes that even though slavery may not have benefitted the planters of the South, it did have major consequences in other areas of America. He believes that the Midwest was a direct benefactor of the South’s slavery, primarily because it provides certain foodstuffs that the failing plantations were unable to provide. In the same vain, James Walvin concluded that modern banking techniques were developed out of the long-distance Atlantic slave trade, namely the need for credit.

But perhaps most importantly, slavery helped drive economic expansion of America and the United Kingdom. Eric Williams, former president of Trinidad and Tobago and an expert on the slave trade, believed that slavery was essentially used as global commodity by the British – it helped forge new trade routes and economic opportunities, a major precursor for British industrialization. He also believed that slave profits went directly toward financing the railways, the most important part of the industrial revolution.

So while slavery wasn't as lucrative for planters as it might have promised, it did seem to benefit the nation as a whole by facilitating expansion and industrial growth.