What areas did the Aztec Empire include?

Many years after the Mexica people first built their proud city, Tenochtitlan (later to become Mexico City), they formed an alliance with two other cities - Texcoco (Tetzcoco) and Tlacopan. This Triple Alliance was to rule the Valley of Mexico until the Spanish arrived. However, over time one city become the most powerful - Tenochtitlan. It would become the heart of the Aztec civilization.

Essentially, Aztec empire history is a history of city-states. As the empire expanded (which it began to do in earnest around 1428) it conquered more cities. Some cities resisted. Others were conquered and began to pay tribute., even the term Aztec is a bit misleading. It's a name that is used for a group of peoples in Central Mexico, but really there wasn't any one people group that was "Aztec". The Mexica people were at the heart of the empire, but there were many other cultures that formed the civilization that the Spanish were to discover.