As is well known, the marriage of Ferdinand and Isabella in the middle of the fifteenth century paved the way for the unification of a reconquered Spain and the dominance of Castilian among its languages. Castilian was a language that would serve the Catholic Monarchs as an ‘imperial instrument’, as Nebrija put it. Such was the allure, such the administrative importance of Mexico that large numbers of Spaniards came to it after the conquest. However, it must be borne in mind that in the early days of colonization the linguistic unity of the peninsula was still in the making. Settlers and soldiers with other dialects and languages also made their way to the New World: people came not only from Castile but especially from Andalucía and Extremadura. Among these people, some, such as the missionaries and the administrators, were well-educated, but there were also substantial numbers who were neither educated nor from the upper social strata. In all, a variety of language practices came to Mexico, some refined, some popular, and these varieties made contact with the Indian languages, especially with Maya and Nahuatl.

These, then, were the key early colonial ingredients. A later one was the importation of slaves from Africa, but it was to become less of a factor in the linguistic development of Mexico than it was in some other countries, such as those of the Caribbean. In Mexico, the African presence was most noticeable in the Veracruz and Acapulco areas, both large ports; there, one still finds vestigial cultural and linguistic influences, though generally the Africans were quick to assimilate and mix with other races, with the result that it is difficult to identify their influence on the modern language very discretely. There were other foreign-language influences upon nineteenth-century Mexico, despite which the country never received the kind of large-scale waves of immigration that left such an imprint on some other countries, particularly Argentina. The single most important influence in modern times is clearly that of the United States; its proximity, its chequered history of interaction with Mexico, the power of the media and the ever-increasing flow of Mexicans across the border, which gathered pace in the second half of the twentieth century, have meant that the influence of US English on Mexico's language has been considerable and increasing.