Final answer:
The primary cause of death among Magellan's crew was disease, as the natives encountered had no immunity to the infectious diseases brought by Europeans. Smallpox, typhus, and measles spread rapidly, leading to high fatality rates among native populations.
Step-by-step explanation:
The main reason why such a large percentage of Magellan's crew did not survive the expedition was due to disease. While hostile natives and lack of food certainly played a role, nothing was as devastating as the impact of diseases like smallpox on populations that had no previous exposure and therefore no immunity. Diseases that were common in Europe, such as smallpox, typhus, measles, and influenza, were brought to the Americas where they spread rapidly among the native populations. The combination of direct conflict, diseases, and the resulting disruption of the native peoples' food sources and lifestyles (such as the indirect effects of livestock destroying crops) led to weakened immune systems and catastrophic death tolls. The Europeans' superior weapons did contribute to some deaths, but the vast majority of fatalities were due to infectious diseases.