[Editorial Note: This post contains images and stories pertaining to child slavery. If you do not wish to view these, do not click through to the full article]

I became a photographer to change the world. It’s just been a little bit harder than I thought it would be.

I grew up in Iran, and by the time I was twelve I had been around the world twice with my family, and had visited twenty countries along the way. I wanted to find a career that would keep me out in that world, and journalism—especially photography—seemed perfect. I saw the role that photography had played in ending the war in Vietnam and wanted to join that cadre of crusading photographers.

But when I joined the staff of National Geographic, my ambitions became somewhat more modest—or realistic: I could illuminate worlds most people would never see. As a journalist, I loved telling stories, and especially loved being behind closed doors in intimate situations that revealed something about the human condition. I tried to get that kind of photograph into every story, no matter how complicated the assignment or vast the terrain.

And they were big: cities (Jerusalem, Los Angeles, London, Hong Kong, Helsinki, Nashville, Shanghai and Venice) and countries (China, Jordan, Thailand and Taiwan). But my later stories on the women of Saudi Arabia, the geisha of Japan, and the science of beauty and love let me make the kinds of photographs I liked best. I was able to enter some very private places indeed—some never photographed before—and share them the world.

But then a newspaper article about Congress passing the Anti-Trafficking Act caught my eye and I knew that contemporary slavery was an issue I had to try to make sense of. It would be the culmination of all my passions and experience.

“21st Century Slaves” is the story about how an estimated 27 million people in the world today live as real slaves—bought and sold against their will, held captive, brutalized and exploited for profit. The trafficking of human beings has become the world’s second-largest criminal activity.

Globalization has made it easier to move goods and money around the world, but tough restrictions on legal migration make it hard for people to move where the jobs are. Ruthless criminals—the mafias of Russia and Albania, the Triads of China and the Yakuza of Japan—are only too happy to help. Tragically, people are likely to end up in debt to their smugglers and are forced to work off their debts as slaves.

It was an under-reported story in this country, and National Geographic had the resources to put together a comprehensive, worldwide look at the issue. Not many organizations could provide the time for research, planning, making connections, gaining trust—and none had—but it was still a magazine story with a real budget for time and money. The Editor, Bill Allen, had reservations: was it the kind of story National Geographic’s readers would embrace? He could imagine subscribers quitting in droves. But he also felt it was a story that he had an obligation to publish.

But if he was worried, I was panicked. How could I pull it off? I hunkered down with the great Illustrations Editor Susan Welchman and we started making lists. What kind of slavery existed and where? Where could I actually see it—and shoot it?

Our list was a catalog of misery. Child labor, bonded labor, organ trafficking, illegal adoption, domestic slavery, agricultural slavery and the commercial sex industry. We researched where it was most visible, and who could take me there. So I set out on my tragic journey.

I went to India because millions of kids work there, the highest number in the world. They are sold or kidnapped into industries like carpet and silk weaving and glassmaking. As a horrible bonus I could also find bonded labor, illegal kidney trafficking and a thriving sex industry. Falkland Road in Mumbai is one of the largest red-light districts in the world, where huge numbers of women are sold, lured and tricked into prostitution. Some enter that world knowingly, but don’t expect to become enslaved, and have no idea what’s in store for them. My Indian assistant Neha and I would spend the day in the brothels—nasty, stinking, sweltering buildings packed with girls and women of every age, clients of all kinds and babies that would grow up with no future but to enter the family business. We’d go back to our car and weep. And return day after day.

It was a short hop up to Nepal, where I found a thriving organization rescuing girls trafficked to India—a small ray of hope. On a quick side-trip to Israel, one of the world’s largest importers of Eastern European women, I photographed a police raid on one of the hundreds of brothels in Tel Aviv. In Thailand, an American religious organization tilting at windmills would prove that once prostitution becomes part of a country’s official economy, it becomes impossible to eradicate or reform. Their attempts to rescue some underage girls, with me in tow, failed. There was always an inexplicable tip-off.

Illegal immigrants can easily end up in debt bondage when they can’t pay their smugglers, and in Italy I found entire Chinese families, babies and all, toiling in factories for luxury leather goods. I was able to grab a picture of them sewing Gucci labels into hats and bags. “Shoot fast and scram,” Cartier-Bresson said—and I did.

Domestic slavery exists worldwide, but tens of thousands of kids are trafficked internally in West Africa. It’s the abuse of a tradition where kids from rural villages were sent to cities to live with relatives in exchange for an education and a chance for a better life. It’s now a professional trafficking operation and the kids end up enslaved. So Ghana and Benin went on the list, and I found 14-year-old mechanics in rags working without rest or pay, and tiny kids balancing huge baskets of fruit and vegetables on their heads, staggering through the markets, selling for their masters.

So is there debt bondage and slavery in the U.S.? Experts estimated that perhaps ten percent of all farm workers here are enslaved. The Coalition of Immokalee Workers in Florida has broken up nine slave rings in the American south, freed over a thousand tomato pickers from debt bondage and successfully taken on huge corporations like Taco Bell and McDonald’s. I went with them on their hunger strike at Taco Bell headquarters, and then to the U.S. Capitol to pick up their Robert F. Kennedy Humanitarian Award—another rare moment of hope.

But let’s talk about Bosnia. Post-conflict societies are often the hardest hit by traffickers, and Bosnia must top the charts. The writer, Andrew Cockburn, came back to National Geographic with tales of a war criminal and sex trafficker so brazen that he taunted the media with statements like “Is it a crime to sell women? They sell footballers, don’t they?” Andrew had visited his medieval-castle-themed motel-brothel, populated by—besides enslaved Eastern European women—caged tigers, bears and pit bulls. Andrew couldn’t get any locals to accompany him out of fear for their lives, but had managed to interview him. I was determined to photograph that face of evil. I’ll call him MM because I’m still afraid of him.

So off to Sarajevo I went. I hired a young local Bosnian Muslim—a dental student before his life had been ripped apart by the war—to drive and interpret for me. I’ll call him J, because he too is still afraid. We spent a couple weeks working together, traveling in his battered car and making up movie plots to pass the time. We drove for hours in UN convoys on brothel raids that were usually thwarted by ubiquitous tip-offs. We cruised by brothels in the countryside looking for evidence and finding it. And we visited shelters for rescued girls (most were underage) run by brave local women defying criminals so bold they would come to the shelter to get their girls back—even though the shelters were under armed guard. The girls were traumatized and broken. One had a nail driven through her hand, another a syringe buried in her arm. I saw one with cigarette burns all over her body.

When the rare brothel raid succeeded, UN forces would storm in, separate the girls from their captors and interview them. Their stories were depressingly similar. Lured from their poverty-stricken homes in Moldova, Romania, Ukraine and such by friends, relatives or others promising good jobs abroad, they were smuggled into Bosnia by well-organized criminal syndicates who then raped them “to test the goods,” tortured them into submission and sold them at open-air markets to brothel owners—who then forced them to be with ten or more men a night in indescribably brutal conditions.  The UN officer would then ask the girls if they wanted to return with them to Sarajevo for help, and a distressing number refused. Too many UN officers had been their customers. I rode back to Sarajevo one night with a 16-year-old who accepted the offer of rescue, and we both cried as she told me her story.

When I had exhausted the official sources it was time to take on MM. A Serbian journalist with major underworld connections met me at a truck stop caf© to warn me: MM was ruthless … death threats … bombings … journalists beaten on the streets … legs blown off … car-bombs. He asked for money for the warning.

But J agreed to come with me, and we nervously drove six hours to Prijador to the Sherwood Castle. We walked in past the heavily armed security guards, introduced ourselves and asked for MM. He soon rushed in, beefy, sweating and offering me his hand. I asked to photograph him and astonishingly, he agreed. I shot him with his caged animals and a stuffed tiger, a former pet—his wife behind me angrily chattering the whole time. J later said she was berating him for cooperating. He invited us for lunch, and too terrified to refuse, we sat down for an agonizing meal. We finally bolted, and on our way out, MM asked for a donation from National Geographic to his zoo.

J and I decided not stay in the Prijador hotel we had booked, and raced the six hours back to Sarajevo, mostly in silence. Our car was followed.

A few months later, J called from Sarajevo. He had been living in fear of MM after the publication of his photograph, and I too had been half expecting him to show up on my doorstep. So with great relief I heard he’d been arrested for trafficking two hundred women. He has, however, escaped.

And so it went for the year it took to produce the whole story. But it took me even longer to recover from searching for evil day after day and finding it. Nothing in my life had prepared me for the ruthlessness, heartlessness—the inhumanity—of trafficking. I was in fear or in tears the whole time. But it’s the most important story I’ve done and generated the biggest response in the history of National Geographic until then.

So maybe I didn’t change the world, but that world changed me—profoundly and irrevocably. I notice things I never did before. I don’t think of prostitution as a victimless crime, and I don’t think that buying stuff really cheap is as fun as I once did. Someone makes that stuff, and in the drive for lower and lower prices, the temptation is just too great: there is no cheaper labor than a slave.

You can see more of Jodi’s work at JodiCobb.com