<P> The Catholic Church during the Age of Discovery inaugurated a major effort to spread Christianity in the New World and to convert the Native Americans and other indigenous people . The evangelical effort was a major part of, and a justification for the military conquests of European powers such as Spain, France and Portugal . Christian Missions to the indigenous peoples ran hand - in - hand with the colonial efforts of Catholic nations . In the Americas and other colonies in Asia and Africa, most missions were run by religious orders such as the Franciscans, Dominicans, Augustinians, and Jesuits . In Mexico the early systematic evangelization by mendicants came to be known as the "Spiritual Conquest of Mexico ." </P> <P> Antonio de Montesinos, a Dominican friar on the island of Hispaniola, was the first member of the clergy to publicly denounce all forms of enslavement and oppression of the indigenous peoples of the Americas . Theologians such as Francisco de Vitoria and Bartolomé de las Casas drew up theological and philosophical bases for the defense of the human rights of the colonized native populations, thus creating the basis of international law, regulating the relationships between nations . </P>

Why did spain send explorers to the new world