The Aztec Empire was an empire that extended its power throughout Mesoamerica in the late post classic period. It originated in 1427 as a triple-alliance between the city states of Tenochtitlan, Texcoco, and Tlacopan. They allied to defeat the state of Azcapotzalco which had previously dominated the Basin of Mexico.
The Aztec Empire extended its power by a combination of trade and military conquest. They had a large well organized and well equipped army. Like a modern army, it was divided into units under the command of officers.
The Aztec Empire controlled its vassal states by installing friendly rulers. They also contracted marriage alliances with ruling families. Their territory reached as far as Pacific Ocean. At the time of the Spanish conquest in 1519, the Aztecs were at the zenith of their power.