From The Penguin History Of Latin America, by Edwin Williamson (Penguin, 2003), Kindle pp. 44-45:
The basis of Aztec dominion was the levying of tribute in the form of goods and labour from tribes defeated in battle. Territory was also expropriated and distributed as private estates to deserving Aztec nobles. To maintain their hegemony, the Aztecs planted colonies in conquered lands and supported these with Aztec garrisons. Tribute-collectors would bring back an abundance of goods to Tenochtitlán, not just staples such as maize or beans but also luxuries and trappings of status that the Aztec aristocracy craved – objects of jade and gold, precious stones, quetzal feathers and jaguar skins. Indeed, Aztec conquests were motivated as much by religious and cultural factors as by purely economic needs. Defeated tribes were forced to add the Aztec deities to their pantheon and to adopt the Nahuatl tongue. A major reason for waging war was the taking of prisoners to be sacrificed upon the altars of the great pyramid at Tenochtitlán. The Aztec gods stimulated belligerence by their unceasing demand for human blood, and it is possible that the purpose of the continual ‘wars of flowers’ against the neighbouring Tlaxcalans was to ensure a steady supply of sacrificial victims rather than conquest as such.
The Aztec nobility were able to live in great luxury by adapting the traditional customs and institutions of Middle American tribal culture to their own advantage. The most effective of these adaptations was in the field of myth and religion, for it was religion that underpinned the unquestionable authority of the Aztec emperor or tlatoani (‘he who speaks’), and provided the rationale for conquest and the imposition of tribute. Religion was a particularly effective tool of imperialism because much of the Aztec religion was common to other peoples of Middle America, all of whom could trace their heritage to the Toltecs, the true founders of Nahuatl civilization. Once the Aztecs had started on their imperial expansion, they took pride in styling themselves the heirs of the Toltecs, a claim which served to give their rule a sacred justification.