12 Diseases That Altered History

Syphilis, hemophilia, and potato blight are among the ills that have changed the world.

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Bubonic plague is mainly a disease in rodents and fleas (Xenopsylla cheopis).

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Malaria. One of the most lethal infectious diseases in history, malaria causes over 300 million cases worldwide and up to 3 million deaths a year. It's one of the earliest examples of the importance of controlling vectors—animal or insect carriers (in this case, mosquitoes)—in preventing the transmission of disease. One of the reasons Europeans managed to colonize Africa, according to Sherman, was that they utilized quinine, an antimalarial drug derived from the bark of the cinchona tree.

Yellow fever. Although vanquished in some countries, this mosquito-borne disease hasn't been eradicated and probably never will be, says Sherman. The disease influenced the building of the Panama Canal, the Louisiana Purchase, and, in fact, the pre-World War II development of the southern United States. "The stereotypes of the lazy, drawling southerner and the energetic, bright northerner were typical characterizations due to disease or the absence of disease," Sherman says. "In the North, mosquitoes couldn't survive overwintering, so there wasn't yellow fever. In the South, on the other hand, you had a population that was either decimated or debilitated by the disease."

Hemophilia and porphyria. As genetic blood disorders, hemophilia and porphyria had serious effects on the crowned heads of Europe. According to Sherman, the rise of Spanish dictator Francisco Franco can be traced to the lack of an heir to the throne because of hemophilia. Another example is the collapse of the Romanov dynasty in Russia, which was due to hemophilia in the family. The czar was debilitated and couldn't take over, setting the stage for the rise of the Bolsheviks.

Many of the British monarchs were unable to manage their kingdoms because of porphyria, which can cause a variety of mental problems, like hallucination, paranoia, and anxiety. Some describe George III's treatment of his American subjects, which helped to trigger the American Revolution, as being in part affected by his porphyric attacks.

Potato blight (cause of the Irish Potato Famine). Sherman expanded the range of maladies to indicate to readers that diseases affect not only humans but also sometimes what we eat. Potato blight had a profound impact because it devastated a staple food that fed much of Ireland in the mid-1800s. Other plant diseases could have similarly far-reaching consequences today, says Sherman. Many agricultural economies focus on a particular crop, so a single disease could be a big threat—and a major historic force. The Irish famine influenced America by generating an influx of Irish immigrants to U.S. cities; those newcomers expanded the Democratic Party, participated in the development of labor unions, and molded the nation's character in numerous other ways.