The Aztecs formed out of an alliance of three major cities in modern day Mexico in about 1430, just 89 years before Cortes and his conquistadors showed up. The Aztec state was very hierarchical, with an emperor at the top and a group of unruly nobles beneath him, just like Europe. And in addition, there was a class of powerful priests whose job it was to keep order in the cosmos. So Aztec religion held that history was cyclical and punctuated by terrible disasters and then would ultimately end with a massive apocalypse. And the job of the priests was to avoid these disasters by appeasing the gods, generally through human sacrifice. The Aztecs extended their control over most of southern Mexico, parts of Guatemala and the Yucatan, and they demanded tribute from conquered people in the form of goods, precious metals, and people to sacrifice. If you're familiar with The Hunger Games, it won't surprise you to learn that this didn't sit very well with said conquered people.