When the Spanish arrived to America in 1942, the Spanish Empire was ruled by the Catholic Monarchs, this is the name used to jointly refer to Queen Isabella I of Castile and King Ferdinand II of Aragon, who got married and unified their kingdoms (Castille + Aragon), and this led to the constitution of the Spanish Empire. They financed Columbus trip towards Western seas.
Once the Spanish had arrived in America, they soon knew the superb economic impact it would suppose for the Empire. But, according to their deep religious beliefs, the King explicitly stated that the main aim of the Spanish in America was to spread the catholic doctrine among the pagan indigenous people living there.
These intentions were even legally formalized in 1512, when Burgos Laws were issued in order to rule the relationship between the Spanish Empire and American population, and the main priority established was the evangelism (or conversion to Catholicism) of the natives .