 One detractor, the abolitionist David Walker, called Las Casas a "wretch... stimulated by sordid avarice only," holding him responsible for the enslavement of thousands of Africans.Other historians, such as John Fiske writing in 1900, denied that Las Casas's suggestions affected the development of the slave trade.Benjamin Keen likewise did not consider Las Casas to have had any substantial impact on the slave trade, which was well in place before he began writing.