 By 1519, the Aztec capital, Mexico-Tenochtitlan, the site of modern-day Mexico City, was one of the largest cities in the world, with an estimated population between 200,000 and 300,000.The first mainland explorations were followed by a phase of inland expeditions and conquest.The Spanish crown extended the Reconquista effort, completed in Spain in 1492, to non-Catholic people in new territories.