In many ways the "Spanish" expeditions across what is now Mexico and Central America were a continuation of the Aztecs own expansionist tendencies. The Spanish entered into a Mesoamerican world dominated by the Aztecs and, in the early years forming their impression of the land, learned about this new world through an Aztec lens. In 1521, what the Spanish knew about Mesoamerica was what they had learned from the Aztecs or enemies of the Aztecs, and they were eager to see (and plunder) the lands they had learned of, or, as Bernal Diaz del Castillo put it:

In the tribute books of Montezuma we saw whence they brought him tribute of gold and where there were mines and cacao, and garments of cotton cloth, and we wished to go to those places whence, we saw from the books and the accounts contained in them... (Carrasco trans. 2008, p. 318-9).

Yet because all of these places the Spanish were learning about were through the Aztecs and other Nahua groups like the Tlaxcala, the Spanish learned the Nahuatl names for them. In the early Spanish works many toponyms and demonyms are sometimes explicitly noted as coming from Nahuas. For example when Diaz del Castillo refers to the Huaxtecs, he notes he calls them this because "for so they [Nahuatl-speakers] call the Indians of these provinces" (p.320). More often the Nahuatl names are simply used without comment, even when the local inhabitants of a region would not have been Nahuatl-speakers, such as when Diaz del Castillo speaks of an expedition to Xoconocho, the Nahuatl name for the Aztec province on what is now the Chiapas-Guatemala border. The people there were majority Zoque-speaking, but a mixed Spanish-Nahua force arrives at a town called Zapotitlan before moving on to Quetzaltanango, and from there to Utatlan, all Nahuatl toponyms reproduced in the Spanish text.

As noted, the forces spreading out from (San Juan de) Tenochtitlan to more disparate parts of what was Aztec hegemony were not solely Spanish, but always included a substantial Nahua portion, which could sometimes dwarf the European component. When Cortes headed for Panuco (occupied by the Huaxtecs mentioned earlier), he set off with "120 horse, 300 foot, and some artillery, and as many as 40,000 native warriors" (Morris trans. 1969, p. 247). As they had been during their conflict with the Aztecs, the Spanish were reliant upon indigenous groups to make up the bulk of their fighting force, in addition to acting as guides, porters, or to simply name the places they were headed.

In other cases, the solidification of Nahuatl was through settlement and not conquest. The state of Zacatecas, for instance, comes from the Nahuatl term for one of the Chichimec groups in the region, but the discovery of rich silver veins in the region led to extensive colonization by Spanish and Nahuas. For instance, one of founders of the city of Zacatecas was Juan de Tolosa, who was married to Leonor Cortes Moctezuma, the illegitmate daughter of Hernan Cortes and Isabel Moctezuma, a daughter of the Emperor Motecuhzoma Xocoyotl. It was not merely prominent Nahuas moving northward though, there were deliberate attempts to settle central Mexican peoples in the wild lands of Gran Chichimeca in the hopes that they would act to stabilize the region. Bakewell, in Silver Mining and Society in Colonial Mexico notes that "the most famous of these migrations was that of some 400 Tlaxcalan families in 1591" (p.35), with groups initially settling near San Luis Potosi but also dispersing further north.

So the template for the world the Spanish encountered was Nahuatl, and the Spanish learned about the world through Nahuas. After the initial defeat of Cuauhtemoc, the Spanish soldified their hold on prior Aztec holdings, and then extended them with extensive use of Nahua forces. At the same time, Nahua-speaking groups were moving throughout the expanding regions of New Spain, sometimes in deliberate efforts to place friendly Nahuas in hostile territory. Already a widely-spoken lingua franca, particularly in central Mexico, Nahuatl became even more widespread with certain toponyms and demonyms derived from that language become the official names under the colonial regime.