Final answer:
The largest loss of population among the Aztecs was due to disease and epidemics, like smallpox, brought by Europeans. This led to a drastic decline in their numbers, which was a bigger impact than war, famine, or environmental challenges.
Step-by-step explanation:
The largest population of Aztecs died off primarily due to disease and epidemics. While war and conflict, famine, and environmental challenges certainly impacted the Aztec Empire, it was the introduction of Eurasian diseases such as smallpox, typhus, and measles, to which the native population had no immunity, that resulted in the most dramatic population decline.
These diseases, brought by European explorers and colonizers, spread rapidly through the densely populated cities via established trade routes, even reaching areas that Europeans had not yet visited. The impact was catastrophic, with statistics showing a rapid descent from an estimated 25 million individuals to around 2 million within the span of just 60 years.
The situation was exacerbated by malnutrition and weakened immune systems caused by the disruptions to agriculture from European settlement. During the Spanish invasion led by Hernando Cortez, smallpox played a crucial role in diminishing the Aztec population, which gave the Spanish a significant advantage, leading to the fall of the Aztec capital, Tenochtitlán.
This resulted in a devastating population decline, with one out of every three native people dying within just ten years. Other factors contributing to the decline included warfare and the invasion by Cortes in 1521.