This paper proposes that mortality rates declined in America from the 17th through the 19th centuries in several stages. From first settlement through the end of the colonial period, high levels of base-line mortality had superimposed upon them epidemics caused by disease agents that require large populations in order to become endemic (measles and especially smallpox). Dysentery and malaria of the named diseases seem to have been the most significant endemic diseases. From the end of the colonial period through the Civil War, mortality nationwide stabilized as measles and smallpox became endemic childhood diseases. Cities did continue to manifest wide fluctuations in death rates, especially those that grew rapidly. Nonetheless, this was not characteristic of the nation as a whole. Between the Civil War and World War I both urban and rural mortality began to decline despite the fact that more migrants than ever flooded the cities from high mortality countries of eastern and southern Europe. The decline was the result first of a drop in significance of endemic named diseases, followed by the non-specific pneumonia-diarrhea complex affecting infants and young children.
Kunitz, Stephen J.
"Mortality Change in America, 1620-1920,"
3, Article 13.
Available at: https://digitalcommons.wayne.edu/humbiol/vol56/iss3/13