In the summer of 1775, facing war with Britain, Colonial America also faced the simultaneous threat of a smallpox epidemic. Inoculation, the technique of fostering immunity by scratching smallpox pus into the skin, was known to be effective, but it was also feared by many. There was the very real chance that those who were recently inoculated would infect others and spread the pox even further. This fear was especially prevalent in New England, where the practice was banned. During the siege of Boston, the pox raged within the city and threatened the Continental Army without. Fearing that inoculating the Army regulars would leave them sick and vulnerable to attack, George Washington opted for quarantining anyone with signs of the disease or a history of exposure. It was a strategy that failed miserably.

As the besieged city suffered, the British began to let selected people - those infected with smallpox - leave, threatening the health of the surrounding American troops. Quarantine was difficult to enforce among a people lately taken with the ideals of liberty and freedom. In desparation, soldiers and citizens took to secretly inoculating themselves for protection. When the British finally gave up Boston, people fled the city in droves to escape the disease, and even the feeblest attempts at containment were no longer possible. The disease continued to spread through Massachusetts. Finally in July 1776, the colony's legislators lifted the ban on inoculation and stemmed the tide of the epidemic - among civilians anyway. Among the army, the ban still held, and smallpox continued to be a problem. Faced with ever growing sick rolls and mortality rates, Washington reversed course in early 1777 and ordered the inoculation of all recruits. We'll never know for certain, but it was a decision that just might have changed the course of the war.

This, and much more, is detailed in Elizabeth Fenn's Pox Americana: The Great Smallpox Epidemic of 1775-82. The first third of the book, detailing the epidemic among the eastern seaboard of Colonial America and its influence on the War for Independence is the strongest and most compelling portion. The primary sources are rich. She doesn't have to resort to speculation and two hundred year old death statistics to make her case. The second third of the book covers the spread of the disease from Mexico to the American West, and since that place in that time was a barely inhabited frontier, not much is left in concrete documentation except for spikes in the death tolls recorded in Spanish church records. Still, she makes a compelling argument for the advance of the disease among the Indian tribes of the western plains as they followed their horse-trading routes. The last portion of the book traces the disease along the Northernmost territories of the New World, from the Hudson Bay company to the Pacific Coast. Again, the primary sources aren't as abundant, but the case for its spread along fur trading routes is strong nonetheless.