The epidemic in the east, for all its gruesome qualities, was mild in comparison to the outbreak that appeared in Mexico City in August 1779 and spread throughout the hemisphere. Fenn doesn't speculate whether there was a connection between the Mexican smallpox epidemic and the British North American one, though New Orleans, where there were a number of American rebels trading throughout the war and where smallpox broke out in late 1778, may have been a junction between the two. What is certain is that "arrival in Mexico City was key to [the virus's subsequent] success" (142). From thence it could be spread by a large transient population of workers, farmers, and other travelers, down to the coasts and up the caminos reals, throughout Spanish America and into the trading networks of its aboriginal neighbors.
The most geographically significant victims of the smallpox were the Shoshones, who carried the variola virus into Canada – and thus into the trading network of the Hudson Bay Company, thereby killing thousands of Cree and Chipewyans – and down the Columbia River to the Pacific Northwest. While exact numbers are impossible to come by, Fenn thinks smallpox killed about 60,000 Native Americans north of Mexico.
Altogether, 130,000 North Americans died of smallpox between 1775 and 1782. Only 10% of them, however, were Anglo-Americans, which helps explain why this episode remains obscure in U.S. historiography, preoccupied as U.S. historians are with the American Revolution. Beyond the limits of the Thirteen Colonies, however, the epidemic was vastly important: it led to a marked decline in marriage ages in New Spain (as Mexicans tried to replace their population losses), compelled the now-diminished Comanche "empire" to make peace with Spain, and allowed the Sioux to supplant the Mandans and the Blackfeet the Shoshones as the premier hunters and traders of their respective homelands. Throughout Indian country, Fenn concludes, smallpox was a "virus of empire" (275).
One point that Fenn does not make as pointedly as she might, and which is particularly useful to students of colonial America, is that the pattern of variola's spread reveals a great deal about transportation and trade in early America. In British North America, smallpox moved by water from seaport to seaport, then spread slowly inland – except in the case of Canada, where the disease moved fairly quickly up the Saint Lawrence River to the Great Lakes. In Spanish America, smallpox spread rapidly north and south from Mexico City, and was carried almost to the Arctic Circle by horse-borne Indian nomads and their trading partners. Fenn's book thus helps confirm and extend April Hatfield's observation (in Atlantic Virginia [2004]) that the British American colonies were more like an archipelago of outposts than a continuous area of settlement, and that the most extensive networks of human contact within the continent were Native American ones. It also reminds us that epidemic disease was - and remains today - one of the most unfortunate side-effects of improvements in trade and communications; the parts of North America that had the best roads or the most mobile populations were also the regions most susceptible to smallpox, while the more isolated settlements of British North America were most effectively able to control the disease.
