Final answer:
The mention of the landing at Zempoalla suggests the drastic effect diseases like smallpox had on indigenous populations, which lacked immunity to them, leading to widespread mortality and influencing historical outcomes like the Spanish conquest of the Aztecs.
Step-by-step explanation:
When the author mentions the landing at Zempoalla, it suggests the significant impact that the spread of disease had on human health, particularly in the context of historical encounters between different civilizations. The event highlights the vulnerability of indigenous populations to new diseases brought by explorers and conquerors. The landing at present-day Vera Cruz in April 1520 included an African slave infected with smallpox. This disease spread rapidly among the Aztec population who lacked prior exposure and immunity to the virus.
Consequently, about half the population of the Aztec capital and the surrounding region died within six months, undermining their ability to defend against the Spanish invaders, who were largely immune to smallpox. This example illustrates the profound and often devastating effects of disease on populations with no natural resistance, and how such events could alter the course of history.