The correct answer to this open question is the following.
Although you do not mention any context or specific reference, we can help you answer in general terms.
Spanish King Ferdinand and de la Casas's perspectives affect history in that they provide a particular approach to what was happening in the Americas.
Ferdinand, the King of Spain, was living in Europe, so far away from New Spain, the conquered territories. The King heard voices that referred to a specific and biased perspective of what was happening in America. That is why Bartlomé de las Casas wrote his version of the story adding strong words such as "slaughter" to really depict how Spaniards were killing native indigenous people.
Bartolomé de Las Casas (1484-1566) was a Dominican Frair from Spain who was decided to defend the rights of the Native Indians in South America. For the noble labor he did, he is known as the Defender of American Indian
Another perspective of history says that King Ferdinand of Spain and Bartolomé de las Casas used to impose the Encomienda system on the premise that conquered land belonged to the Spanish crown, under the service of God. King Ferdinand knew about the many raw materials and natural resources from the Americas and was urged to exploit those resources to the benefit of Spain. Bartolomé de las Casas owned many Encomiendas on the island of Cuba. So he was not only interested in evangelization and in the conversion of American Indians into Catholicism, he loved getting rich and that's what he did through the Encomienda system.
