Aztec is a term used to refer to certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who achieved political and military dominance over large parts of Mesoamerica in the 14th, 15th and 16th centuries, a period referred to as the Late post-Classic period in Mesoamerican chronology. Often the term "Aztec" refers exclusively to the people of Tenochtitlan, situated on an island in Lake Texcoco, who called themselves Mexica Tenochca or Colhua-Mexica. Sometimes also includes the inhabitants of Tenochtitlan's two principal allied city-states, the Acolhuas of Texcoco and the Tepanecs of Tlacopan, who together with the Mexica formed the Aztec Triple Alliance which has also become known as the "Aztec Empire". In other contexts it may refer to all the various city states and their peoples, who shared large parts of their ethnic history as well as many important cultural traits with the Mexica, Acolhua and Tepanecs, and who like them, also spoke the Nahuatl language. In this meaning it is possible to talk about an Aztec civilization including all the particular cultural patterns common for the Nahuatl speaking peoples of the late postclassic period in Mesoamerica. From the 12th century Valley of Mexico was the nucleus of Aztec civilization: here the capital of the Aztec Triple Alliance, the city of Tenochtitlan, was built upon raised islets in Lak Texcoco. The Triple Alliance formed its tributary empire expanding its political hegemony far beyond the Valley of Mexico, conquering other city states throughout Mesoamerica. Aztec is also an acronym for A to Z Technologies.