Merchants from Brazil, Cuba, North America and the British West Indies traded goods grown by slaves on plantations, for more slaves.
He took a remarkable stand against slavery in the countdown to the American Civil War – but opinion differs about his methods.
The most hated president in US history could teach our new leader a few things.
A growing roll call of books, films and television shows are focusing on the legacy of slavery.
The number of people in slavery across the world is on the rise, or maybe researchers are just getting better at counting.