Final answer:
The spread of infectious diseases significantly weakened the ability of Native Americans to resist European invasion. Up to 90 percent of Native Americans died from European diseases due to their lack of natural resistance and malnutrition caused by disruption of their food sources.
Step-by-step explanation:
When European conquerors reached the Western hemisphere, they brought with them disease-causing bacteria and viruses, which triggered epidemics that devastated Native American populations who had no natural resistance to these European diseases. The lack of exposure to European diseases and livestock, coupled with malnutrition caused by disruption of Indigenous peoples' food sources, weakened their immune systems and made it harder for them to fight off infectious diseases. As a result, up to 90 percent of Native Americans died from infectious diseases after the arrival of Europeans.