The five films in the WHY SLAVERY? series, making their U.S. premiere on GBH WORLD’s Doc World this month, shed light on the millions of men, women and children living in the shadows of modern slavery across all corners of the world.

“About 40 million people are currently living as slaves—more than at any other time in history—and that is a conservative estimate,” said Mette Hoffmann Meyer, executive producer of the films and chief executive of THE WHY FOUNDATION, a Danish nonprofit whose main purpose is to donate documentaries about human rights to underserved and fragile countries. The films will be available on YouTube and the PBS app on December 10 in recognition of International Human Rights Day.

Through interviews with slaves, recruiters and slaveholders, the films bring viewers up close to harrowing realities—from ISIS terrorists seizing and trafficking Yazidi women fleeing genocide in northern Iraq, to Kenya where girls are lured into servitude in the Middle East, and then to Russia where the North Korean government sells its people to fund its regime.

In Maid in Hell, the owner of a business that recruits Kenyan women to work in harsh conditions in Lebanon and takes away their passports and phones, openly describes his business and refers to it as “normal.”

“He doesn’t see it as something wrong. It’s just the way of the world,” said Hoffmann Meyer, adding that in most settings, enslavement has been going on for centuries and has deep roots in the culture.

In North Korea’s Secret Slaves: Dollar Heroes, undercover footage and powerful testimonials reveal that the government steals the income of its slaves in Russia, China and Poland. I Was a Yazidi Slave captures the stories of girls struggling to recover from the sexual violence and trauma suffered at the hands of ISIS. Selling Children investigates the incalculable numbers of children in India who are bought and sold as slaves, deprived of an education and doomed to a lifetime of working in stone quarries.

“The most shocking thing is the systemic nature of slavery—how widespread it is and how accepted it has become,” said Hoffmann Meyer. The idea for the series came to Hoffmann Meyer when she was at the U.N. General Assembly to launch the foundation’s WHY POVERTY? films. “I heard President Obama’s speech about modern-day slavery,” she said.

“I thought, if he spends 40 minutes talking about slavery in this setting, it’s probably a much bigger issue than I knew.”

“WHY SLAVERY? is a perfect fit for GBH WORLD,” said Chris Hastings, GBH WORLD executive producer. “It surfaces and humanizes a very complex issue that is often ignored.”

The WHY SLAVERY? series has been shown around the world in multiple languages, with about 80 million viewers per film on local television, in government agencies, in the countries involved and even at the Vatican.

Hoffmann Meyer said she hopes that knowledge prompts action. “Once you’ve seen these films, you can’t not think about these people.”

Watch the series, which starts Sunday, December 12 at 10pm on GBH WORLD.