What motivated the spain's conquest of central and north america?

Spanish conquest of Central and North America was motivated by the Spanish Monarchy through the House of Castille.  It was carried by the Spanish Conquistadores and Catholic priest who also followed these expeditions for conquest.  The main reasons for the conquest were to increase trade and to convert the indigenous people to the Catholic faith.  It started when Queen Isabella supported Christopher Columbus in voyage to reach India by sailing westward.  This was followed by Spanish conquest of Mexico, Peru, Rio De Plata and Paraquay.