Hernán Cortés might have wanted to become an emperor, but Spain already had one.
Holy Roman Emperor Charles V, who was king of Spain from 1516 to 1556, wanted to keep tight control over any Spanish colonies. He carefully kept Cortes from acquiring any real power over the lands he had conquered.
Instead, in 1535, Charles made Mexico a viceroyalty called New Spain. He named Antonio de Mendoza (c. 1490-1552) as the first viceroy, or royal governor.
Under Mendoza and subsequent viceroys, the government and economy of Mexico was organized by encomiendas. These grants gave a few Spanish settlers large tracts of land, with jurisdiction over any Native Americans who lived there.
Treated little better than slaves, Native Americans were required to pay tribute to the Spanish.