The Aztecs are a playable civilization.
Under a succession of ambitious kings they established a dominion that eventually stretched over most of present-day Mexico. By commerce and conquest, Tenochtitlan came to rule an empire of 400 to 500 small states, comprising by 1519 some five to six million people spread over 80,000 square miles. Valor in war, notably in the feared Jaguar Warrior formations, was the surest path to advancement in Aztec society, which was caste- and class-divided but nonetheless vertically fluid. The priestly and bureaucratic classes were involved in the administration of the empire, while at the bottom of society were classes of serfs, indentured servants, and outright slaves. The incredible story of a wandering tribe that was able to build an empire in one century (from the beginning of the 14th century to the beginning of the 15th) can be largely explained by three main factors: the Aztec religion, the thriving trade routes centered on Tenochtilan, and Aztec military organization. In 1502 the ninth emperor Montezuma II (1502-1520) succeeded his uncle Ahuitzotl as the leader of an empire that had reached its greatest extent, stretching from what is now northern Mexico to Honduras and Nicaragua. The Aztec empire was still expanding, and its society still evolving, when its progress was halted in 1519 by the appearance of Spanish adventurers.
For all its apparent strength, the Aztec Empire had vulnerabilities that the Spanish were able to exploit. Aztec rule was based upon a system of tribute and fear over the surrounding peoples; every year, they were forced to pay the Aztecs money, goods, and a supply of captives to be sacrificed on the altar. Taking advantage of this resentment of their Aztec overlords, the tiny Spanish force was able to attract a massive army of some 30,000 Mesoamericans of many different tribes. After mistaking the Spanish for gods and inviting them into Tenochtitlan, Montezuma was taken prisoner by Hernando Cortes and died in custody. Montezuma's successors, Cuitlahuac and Cuauhtemoc, were unable to stave off the force raised by the conquistadors and, with the Spanish sack of Tenochtitlan in 1521, the Aztec empire came to an end.