Final answer:
Smallpox was the disease that decimated Native American populations, as they had no immunity to it. Introduced by Europeans, it caused catastrophic losses among indigenous peoples, significantly aiding European conquest of the New World.
Step-by-step explanation:
The disease that decimated the Native American populations due to a lack of immunity was smallpox. When Europeans arrived in the Americas, they brought with them a host of diseases to which the indigenous populations had never been exposed. Among these, smallpox was particularly virulent and devastating. Native American populations suffered catastrophic losses because they had no natural resistance or immunity to this and other European diseases. The impact of smallpox on Native Americans was one of the most severe population disasters in human history, with some estimates suggesting up to 90 percent of the Native American population perished as a result of this and other infectious diseases introduced by Europeans.
Factors contributing to the high mortality rates among Native Americans also included environmental disruption, weakened immune systems due to malnutrition, and rapid spread of diseases in densely populated regions. These elements exacerbated the deadly impact of diseases like smallpox on indigenous communities. The lack of prior exposure to European diseases, coupled with subsequent social and environmental stresses, led to immense population losses that profoundly reshaped the Americas.
The tragedy of this enormous loss of life has marked a significant event in global history, underlying the asymmetry of disease immunity between Europeans and Native Americans which played a pivotal role in the eventual conquest of the New World. The history and consequences of these epidemics remind us of the dramatic effects that disease can have when introduced to populations lacking immunity.