Each day, 27 million people cry out in pain, anguish and frustration. Yet no one hears them, for they huddle at the margins of society–voiceless, unseen and essentially powerless to alter their fate. They are the slaves of the 21st century.

That the contemporary world would condone slavery of any kind probably surprises and shocks most Americans, who still shoulder the burden of their own historical connections to that nefarious institution and its ongoing legacy in U.S. life.

In truth, though, slavery has plagued humanity for millennia. The latest versions — ranging from forced labor to commercial sexual exploitation, usually grouped under the label of “human trafficking” — afflict the largest number of people in history.

I remember listening to a colleague’s sad tale years ago about the loss of her close friend to probable slave-traders. Snatched from a marketplace in a southern French city, the young woman never reappeared. At the time, I hastily dismissed the incident as an aberration.

But later on, in 1991, I began conducting some research into the subject and found disturbing evidence. My longstanding interest in Haiti, specifically, drew me to the plight of the so-called restavek children in that country. Restavek was simply a kind way of describing virtual slavery. In some cases, the children were born of sharecroppers who sought a better life for their offspring by sending them to live with landowners in urban areas. In other cases, the children were indentured or simply entrusted to strangers. Some enhanced their lives; most did not. More than 100,000 Haitian children found themselves in those reprehensible conditions.

Subsequently, the global-slavery problem has mushroomed. Each year, according to U.S. government estimates, traffickers move nearly a million people across international borders, including as many as 20,000 into the United States. The U.S. Department of State’s recently released Trafficking in Persons Report shares one victim’s story:

“Like many West African women smuggled or lured into Italy with the promise of jobs, Mercy was forced into prostitution to earn her freedom. She was able to escape with the assistance of a religious order. Escape did not end her nightmare. Three weeks after speaking publicly to human-rights groups about her experience, her sister was reported dead in Florence, true to the threats made by her captors.” Still, Mercy has an advantage over most 21st century slaves: She has found freedom.

What could possibly inspire such a gross demonstration of people’s inhumanity toward each other?

Kevin Bales, director of Free the Slaves, a non-profit organization, and the author of Disposable People: New Slavery in a Global Economy, traces slavery’s resurgence to several factors:

“Firstly, the world’s population has tripled since 1945. Secondly, economic change and globalization have driven rural people to the cities and into debt. These impoverished and vulnerable people are a bumper crop of potential slaves. Finally, government corruption is essential. When those responsible for law and order can be made to turn a blind eye through bribes, the slave-takers can operate unchecked.”

Bales goes on to note that the new slavery is marked by a pronounced shift in the basic economic equation of exploitation: The cost of slaves has dropped significantly. For example, an agricultural slave costing $1,000 in the mid-1800s (approximately $50,000 in current prices) sells for about $100 today. That leaves the contemporary slave at much greater risk. Unlike the expensive slave of yesteryear, today’s typical slave is, in Bales’ words, “cheap and disposable.”

Nations cannot allow the travesty of slavery to continue. They must act to turn the tide on one of the most distressing and tragic human-rights challenges of any age.

Solutions will not come easily, but they necessarily start with increasing public awareness that prompts the only appropriate consensus: Slavery must end. Then the task will fall to political leaders to improve strategies, expand resources to fight slavery and criticize lackluster efforts by nations that profess to condemn it. I join Bales in asking, “Where are the United Nations Slavery Inspectors?”

All who live in freedom have a responsibility to speak for, focus attention on and act to alter the fate of the 27 million who suffer under the scourge of slavery.