No Resistance.

Native Americans had no natural resistance against deadly European diseases such as smallpox, measles, bubonic plague, influenza, and whooping cough. Diseases spread like wildfire in the "virgin soil" conditions of the Americas. Epidemics occurred in the New World in 1520-1524, 1564-1570, 1586, 1588, and 1592-1593. In the Americas, Indians generally enjoyed a better diet and healthier surroundings than did the average European. But because they encountered these diseases for the first time when Europeans touched American shores (and therefore had built up no immunities), they died quickly and in large numbers. Native people who never saw any Europeans still encountered diseases as infected Indians from other groups traveled around the countryside in the course of everyday life. As Europeans arrived in America, they often settled in unoccupied areas that Native Americans had cleared. In many cases these Indians had died from diseases, thus leaving a...