The history of the spread of disease in the New World is intimately tied with the history of the North American Frontier. Famous diseases like smallpox and measles, along with other ailments like tuberculosis, malaria, and influenza (among others), significantly contributed to Native American population declines beginning with the Spanish conquest of Central America (1).

Old World diseases had never been seen in the New World, and Native American populations therefore had little natural immunity against such pathogens (2). This contributed to massive Native American mortality in the Spanish conquests of Central America, with some estimates as high as 90% mortality rates. This is probably an overestimate, with a more accurate count being closer to 30-50% (3). Despite the massive death attributed to disease, it seems that during the Spanish conquests of the early 16th century, the infections were not intentional (4). In his Historia de los Indios de la Nueva España, Fray Toribio de Benavente, observed, along with many contemporaries, that the natives were becoming less and less numerous. To this effect, de Benavente attributes “ten plagues,” the first of which is smallpox beginning in 1520 (5). Livi-Bacci goes on to discuss that contact with Europe, along with smallpox, brought “measles, diphtheria, rubella, and mumps,” which are all diseases that can effectively spread in close-quartered populations, like those of Native American cities in Central America.

Thus, the Spanish inadvertently brought novel diseases to unprepared and unaware populations of the New World, and once established, the diseases were rampant. Smallpox was especially effective at culling Native American populations because, as Alexander von Humboldt reported, it would strike on a regular cycle of 16-18 years (5). With that in mind, it is easy to see how devastating these diseases could be; striking in consecutive waves, each time killing a significant portion of the population. This repetitive nature of infection was indeed a contributing factor in the Spanish conquests, as seen in the deteriorated population encountered in 1521 by the Spanish force under Cortés (6). It is also important to remember that the fate of Native American populations was not solely due to the impact of disease, but was sowed by biological factors in concert with social and demographic factors (7).

One (alleged) example of conspiracy to inflict casualties by using smallpox is seen during the Seven Years War by the British stationed at Fort Pitt in 1763. Whether British soldiers did intentionally infect Native Americans is still somewhat debated, but does present an interesting history of the notion of biological warfare. Most famously from this instance, the letters between Sir Jeffrey Amherst and Colonel Henry Bouquet are particularly interesting. The British garrison of Fort Pitt had been struck by smallpox, with the fort’s commanding officer, Captain Simeon Ecuyer, reporting his concerns about the disease spreading throughout the fort’s population in a letter dated 16. June 1763. “We are so crowded in the fort that I fear disease…I cannot keep the place as clean as I should like; moreover, the small pox is among us.” Captain Ecuyer’s concerns were forwarded to Sir Jeffrey via Colonel Bouquet in a letter dated 23. June 1763, “unluckily the small Pox has broken out in the Garrison [at Fort Pitt].” The deliberate infection of smallpox was not explicitly dictated by Sir Jeffrey, or the Fort’s officers, but was recorded in the diary of William Trent, a trader. Trent reported that two Natives asked the British at the Fort for “‘a little provisions.’” A request which the British responded to by giving “‘them two Blankets and an Handkerchief out of the Small Pox Hostpital. I hope it will have the desired effect’” (8). Sir Jeffrey would have approved of this missive, as confirmed by a postscript to a letter dated 7. July 1763, in which Sir Jeffrey asks Colonel Bouquet, “Could it not be contrived to Send the Small Pox among those Disaffected Tribes of Indians? We must, on this occasion, Use Every Stratagem in our power to Reduce them.” Colonel Bouquet responded on 11. July 1763 that he would attempt to spread smallpox to the natives, but included his anxiety of contracting the disease himself (8).

Further effects of disease on Native American populations were seen in the American Frontier Wars, which effectively lasted from early European settlements in North America in the 17th century, through the conflicts of the American west into the late 19th and early 20th centuries. Due to its time frame, the conflicts involving Native Americans on the American Frontier are more effectively split between pre- and post-American Revolution, the former including the example of Fort Pitt above. One example of smallpox in the American Frontier Wars is recorded in a letter dated 15. January 1891 from Former Indian Agent V. T. McGillycuddy to General Leonard Wright Colby: “[The Ghost Dance] was only the symptom of surface indication of a deep-rooted, long-existing difficulty; as well treat the eruption of smallpox as the disease” (9). This correspondence does not imply an intentional infection of smallpox, but does confirm its existence in the Native American population. Smallpox presumably played a similar role in assisting in quelling native resistance, as it had in the 16th century, and may have therefore contributed to the declining populations of the Native American tribes of the American west, such as the Sioux and Lakota.