With the realization that the Americas represented regions of the Earth of which the Europeans were not aware earlier, there arose intense speculation over the question whether the natives of these lands were true humans or not. Together with that went a debate over the (mis)treatment of these natives by the Conquistadores and colonists. The main impetus for "Sublimis Deus" was a council held by prominent Missionaries in Mexico in 1537, including Archbishop Juan de Zumárraga, Bartolomé de Las Casas and Bishop of Puebla Julian Garcés. They discussed the methods of converting the natives, especially the Franciscan practice of mass baptism. Basing a recommendation to the pope on Las Casas' treatise on how to convert the Indians, "De Unico Vocationis Modo", they sent a letter to Rome with Dominican friar named Bernardino de Minaya (born c. 1489). In 1537, Minaya arrived in Rome and pleaded his case on behalf of the Indians.