[Content Note: Slavery; exploitation; racism; colorism; violence; rape.]
At CNN: Slavery's Last Stronghold. "Mauritania's endless sea of sand dunes hides an open secret: An estimated 10% to 20% of the population lives in slavery."
I'm not even going to excerpt it. Just go read the whole thing. I also recommend the videos, if you're able to watch them.
Here's how you can help.