While technological superiority, military strategy and forging local alliances played an important role in the victories of the conquistadors in the Americas, their conquest was greatly facilitated by old world diseases: smallpox, chicken pox, diphtheria, typhus, influenza, measles, malaria and yellow fever. The diseases were carried to distant tribes and villages. This typical path of disease transmission moved much faster than the conquistadors, so that as they advanced, resistance weakened. Epidemic disease is commonly cited as the primary reason for the population collapse. The American natives lacked immunity to these infections.