Final answer:
American Indians lacked immunity to European diseases due to no previous exposure, and this, combined with factors like malnutrition, led to high mortality rates compared to Europeans, who had developed resistance over time.
Step-by-step explanation:
American Indians often died of diseases that did not kill Europeans because they had not been previously exposed. The lack of prior exposure meant that Native Americans had not developed immunity to the diseases that Europeans brought to the Americas. Diseases like smallpox, typhus, measles, and influenza had a devastating impact on Native populations who lacked both genetic and acquired immunity.
Over the centuries, Europeans had been exposed to these diseases and, as a result, developed resistance either through survival of the disease or through genetic evolution. Unlike the European settlers, Indigenous peoples did not have contact with the same diseases or with domesticated animals that carried them and thus had not built up any form of resistance. The subsequent exposure to new diseases, combined with factors like malnutrition and weakened immune systems, exacerbated the mortality rates among Native American populations.