After investigating the presence of slavery around the world over the past fifteen years, specialist economist Siddharth Kara has come to a shocking conclusion: there are more slaves today than there were over the hundreds of years of slave trafficking that took place between the 16th and 19th century.
Over 350 years, 13 million slaves were bought and sold by traders; today, there are approximately 21 million people working as slaves around the world, according to figures provided by the UN's International Labour Organisation.
But contrary to several centuries ago, slavery is now illegal in every country around the world.
As part of his research, Siddharth Kara toured 51 countries and spoke to around 5,000 victims of slavery before drawing up his disturbing findings in the book Modern Slavery.
According to the British economist, human trafficking has become the third most lucrative activity on the black market, behind the illegal sales of weapons and drugs. As he explains to the Guardian:
"It turns out that slavery today is more profitable than I could have imagined. Profits on a per slave basis can range from a few thousand dollars to a few hundred thousand dollars a year, with total annual slavery profits estimated to be as high as $150bn."
Kara estimates that while victims of sex trafficking only make up around 5% of modern slaves, the illegal industry accounts for around half of the total profits of slavery today.
The average profit generated by a victim of sex trafficking is around $36,000 per individual over one year, compared to around $3,978 for victims exploited in other ways.
"Slavery is happening right under our eyes"
While sex trafficking is probably the first form of modern slavery that comes to mind, men and women around the world are being sold into a large number of industries that feed the global economy, such as fashion, beauty, seafood and commercial sex.
As the Guardian states:
"Slavery is happening right under our eyes. In industries such as construction, agriculture, fishing, domestic work and hospitality it's particularly rife."
A UN global report from 2016 details the many forms of slavery which include forced labour, child soldiers, removal of organs, forced marriage and selling children.
The most shocking fact of all is that the experts estimate slavery could be eliminated within two decades. As professor of contemporary slavery at the University of Nottingham and co-author of the global slavery index Kevin Bale states:
"It is my belief that we could end slavery at a cost of as little as $23bn... slavery can be a thing of the past, it is just a question of the political will and determination to do it."