(CNN) – On Sunday, CNN Digital released a special report called “Slavery’s Last Stronghold.” It focuses on current-day slavery in Mauritania, a West African country where an estimated 10% to 20% of people are enslaved. In 1981, Mauritania became the last country in the world to abolish slavery. It didn’t make owning a person a crime until 2007. Work on this story started 11 months ago, after we stumbled upon a few of those statistics. As part of  The CNN Freedom Project, a multi-year effort to report on modern slavery, we began talking with anti-slavery organizations and government workers who deal with Mauritania in hopes that we could get a sense of what life is like in this place where slavery is so shockingly common. Eventually we found SOS Slaves, an abolitionist group in Mauritania that was founded by a former slave owner and a man whose family was enslaved. Think about that for a second: A slave and a slave owner came together to start an organization that is now trying to liberate people in a place where slavery is arguably more intractable and more common than anywhere else on Earth. It’s such a powerful symbol of hope, cooperation an...