De las Casas believed that the Spanish conquistadors were mistreating the Native Americans, and his 'A Short Account of the Destruction of the Indies' exposed the terrible things the Spanish had been doing in the Americas. This paper caused quite a stir in Europe, as no one had known what the conquistadors had been doing, and as a result, laws were passed to help the natives. I hope that this is the answer that you were looking for and it has helped you.