Final answer:
The significant population change in Mexico during the age of exploration was a decreased population due to European diseases, warfare, and exploitation of resources. The lack of immunity among indigenous populations to diseases like smallpox resulted in high mortality rates, decimating the Aztec population from approximately 25 million to less than 2 million in less than a century.
Step-by-step explanation:
During the age of exploration, one significant population change that took place in Mexico was a decreased population due to devastating epidemics brought by the Europeans. The arrival of Europeans during the age of exploration brought with them diseases to which the indigenous populations had no immunity. Diseases such as smallpox, measles, and influenza spread rapidly among the native people, leading to high fatality rates and a dramatic decrease in population. In the Aztec heartland, the population dropped from about 25 million before the Spanish conquest in 1519 to less than 2 million by 1580. This sharp decline was exacerbated by warfare and the exploitation of resources, which further stressed indigenous communities.
The primary cause of this population change was the introduction of European diseases to which the Native American populations had no prior exposure or resistance. This led to widespread epidemics and high mortality, often referred to as a catastrophic depopulation.