children aged less than 5 years. By the end of the century, that percentage was only 1.4%. In 1900, the three leading causes of death were pneumonia, tuberculosis, and diarrhea, which (together with diphtheria) caused one third of all deaths. Of these deaths, 40% were among children aged less than 5 years. At century's end these diseases were scarce. Heart disease and cancers accounted for more than half of all deaths, with only 4.5% attributable to infectious disease.
The 20th century witnessed a 30 year increase in life expectancy.