The number one reason is the catastrophic impact of germs, which is like a mind-boggling science fiction. The majority of the victims are hidden in the interiors of the Americas, having caught diseases from indigenous peoples. These undiscovered areas won't be known for a century, causing a population collapse.
The Atlantic Slave Trade mixes centuries of human bondage with violence, economics, commerce, geo-political competition, liberty, morality, injustice, revolution, tragedy and bloody reckonings. That sounds like a lot, yet this show merely scratches the surface of this enormous subject.