There are, shockingly, more people in slavery today than at any time in human history - but campaigners think the world is close to a tipping point and that slavery may be eradicated in the next 30 years.
The estimated number of people in slavery - 27 million - is more than double the total number believed to have been taken from Africa during the transatlantic slave trade.
Ship records make it possible to estimate the number of slaves transported from Africa to the Americas and the Caribbean, from the 16th Century until the trade was banned in 1807 - and the figure is about 12.5 million people.
The figure of 27 million slaves today comes from researcher Kevin Bales, of Free the Slaves - who blames the huge figure on rapid population growth, poverty and government corruption.
Many people still think of slavery as a thing of the past, but it exists in many forms, on every continent - ranging from sex and labour trafficking, to debt bondage where people are forced to work off small loans.
But the International Labour Organization (ILO) - whose figure of 20.9 million people worldwide in forced labour does not include bonded labour - believes slavery can be completely eradicated.
The momentum has been growing for the last 10 years, says the ILO's Beate Andreas, pointing to a "growing movement and growing leadership on the part of key countries to take action".
She compares this struggle to the battle against HIV, where it took a number of years to generate the momentum and the commitment needed to overcome the epidemic.
Slavery is already illegal in every country in the world.
"We have not quite reached the tipping point, but it's much more difficult for countries and companies to get away with forced labour nowadays," Andreas says.
"There is reason to be optimistic. We have seen a sweeping change in recent years in terms of legislation and better regulation.
"There's a clear sign that more companies are becoming aware, and more governments are willing to take action. If we have the critical mass of leaders ready to take action, then it can be eradicated."
Bales says there was a time when law enforcement agencies knew how to deal with a truck full of drugs, but lacked clear procedures for dealing with a truck full of people. This is changing, he says.
BBC News - A tipping point in the fight against slavery?
I find it hard to believe that more people today are slaves than the number of Africans shipped across the Atlantic hundreds of years ago. It may be true, because there's more people in the world than ever. But the numbers are shockingly astounding.
I have doubts that slavery would ever be fully eradicated. It may be cracked down a lot more, but there will always be a pimp somewhere kidnapping young girls to work the streets, a business owner looking for slave labor for his selfish needs. And like this article points out, poverty is the biggest issue and it is not easy to eradicate that. I'd like to see poverty be a distant memory, but I'm not that optimistic.
Here's a link that explains why poverty can lead to slavery: BBC - Ethics - Slavery: Why slavery persists