An Attempt to do Good that Led to Great Evil
Las Casas gave the Spanish, and later the rest of Europe, a new and novel justification to enslave other human beings: their race. In this conception, Africans were marked out as fit for enslavement because they were Africans, period. Las Casas eventually called for the abolition of all slavery. By then, however, the cat was out of the bag. Europeans embraced his original idea of race as justification for slavery, and ignored his later retraction. The result was the transatlantic African slave trade.
It lasted for almost four hundred years, from the sixteenth to nineteenth centuries. Twelve to fifteen million Africans were sent to the New World for a life of slavery that that was often dark, cruel, brutal, and short. At least for those who survived the horrific Middle Passage from Africa to the Americas, in which millions perished. That was just the tip of the iceberg. For every single African who boarded a slave ship, up to five more perished in the violence that surrounded the capture of slaves and their transportation to the coasts and slave ships.