Bartolomé de las Casas was a discoverer of the New World and an extreme advocate for Native American rights. However, this tolerance came at an extreme cost to the Africans, whom he said could do four times as much work as Native Americans. This statement greatly empowered the triangular trade. Bartolomé first tried to be a political advocate for the Native Americans, but his many experiments to integrate and assimilate them into colonial society failed. After he was the first minister to be ordained in the New World, he began writing. His works, again preaching the fairness the Natives deserved, shocked most England officials. However, he got some support from Holy roman Emperor Charles V, and made great strides in the movement to treat Native Americans fairly, albeit at the cost of African slaves.
http://oregonstate.edu/instruct/phl302/philosophers/las_casas.html