Origins
The Aztecs originated from three different nomadic tribes, the Mexica, the Texcoca, and the Tepaneca, that settled in the basin of Lake Texcoco around the 13th century. Despite sharing a same language (Nahuatl), and a similar culture, these emerging city states often warred with each other, until an alliance was made between them, known as the Triple alliance. This alliance gave way to what would eventually become great and powerful Aztec Empire.
Military Might
The Aztec Empire had no standing army; as such it had relied on drafting their population in times of raiding, ward or conquest. Starting at their teenage years, the young Aztec warriors in the city capital of Tenochtitlan were first taught how to survive the harsh land and after reaching maturity, they were taught the art of war. The usage of colorful and highly decorated armor denoted the ranking of the soldiers, but most notable were the helmets they wore which were in the shape of the Eagle or the Jaguar, believed to be used as an intimidation tactic. In terms of weapons, scarcity of valuable ores meant that instead of using metals, they used obsidian. This was used in the dreaded weapon known as the Macuahuitl, a wooden club with obsidian blades attached. It was known to be remarkable brutal and efficient in battle, able to decapitate humans easily.
Religion
The Mexica people established a pantheon of gods made of conjoining their mythological beliefs with those of their allies and of the conquered neighboring tribes. To worship them, giant pyramids were erected to bring one closer to the gods. Priest held an extremely large role in society. There were the ones who determined who the next leader of the empire was to be, what neighbor to conquer next, and even what types of foods would be grown and what animals would be hunted throughout the year. One particularly consequential decision made by the priests was that soldiers had to capture their enemies instead of killing them if they wanted to move up in rank. The result was numerous prisoners that would then be used as a sacrifice to the Gods. Common practices of a sacrifice was to remove the heart, the blood was let to pour over the stairs of the pyramid, and lastly the bodies were subsequently flayed.
Collapse
The never ending need to appease their gods meant that human sacrifice was rife in Tenochtitlan. As a result, disease became rampant. In addition, food shortages arose due to lack workforce and a series of devastating droughts. By the early 16th century, the Aztec empire was reduced to no more than a shadow of its former self. The final blow to the empire would be the arrival of Hernando Cortez, a Spanish conquistador, and his expedition force. Cortez was entranced with the large amount of gold there. Motivated by this lust for gold and disgust over the “heretical” ritualistic sacrifices, Cortez teamed up with neighboring enemies of the Aztecs and set upon the city of Tenochtitlan. The result was a massacre. An estimated 500,000+ natives died, thus ending the reign of the Aztecs. In the ruins of the once great city, however, the Spanish started building what is now Mexico City.