What was the primary reason for the dramatic decline in the native population of Tenochtitlan following the Spanish conquest?

The primary reason for the dramatic decline in the native population of Tenochtitlan following the Spanish conquest was disease. When the Spanish arrived in Mesoamerica, they brought with them various diseases, including smallpox, which were previously unknown to the indigenous populations. These diseases had catastrophic effects, as the native people had no immunity to them, leading to widespread mortality.

The outbreak of smallpox, in particular, spread rapidly through the population, decimating the inhabitants of Tenochtitlan and surrounding areas. This was compounded by the fact that the societal disruptions caused by the conquest made it difficult for those who survived to access food and medical care. While war and starvation also contributed to population decline, the overwhelming impact of disease was the most significant factor, accounting for a considerable percentage of the casualties during this period.

Overall, the devastating effects of European diseases played a critical role in the subsequent demographic collapse of native societies in Tenochtitlan and beyond.