Number of reported cases of smallpox in the United States 1900-1952

In the history of the United States, smallpox played a pivotal role in shaping the direction of the country's development. When Europeans first arrived in the Americas, they unintentionally introduced smallpox to the continent and the disease helped to wipe out as much as 95 percent of indigenous Americans. This was one factor that allowed European settlers to colonize the continent with relative ease, although the disease remained active in the Americas until the second half of the twentieth century. The number of smallpox cases in the United States fluctuated between 1900 and 1930, with as many as 110,000 reported cases in 1920, however the number of cases fell sharply in the 1930s, and there were no cases at all in the United States from 1950 onwards. In 1980, the World Health Organization declared the disease to be successfully eradicated on a global scale, making it the first infectious disease to be wiped out by intentional human activity.