Just as there are many ways for microbes to infect a body, there are many ways for epidemics to play out in the body politic. Epidemics can be short-lived or protracted, or, like the Justinianic plague, recurrent. Often, they partner with war; sometimes the pairing favors the aggressor, sometimes the aggressed. Epidemic diseases can become endemic, which is to say constantly present, only to become epidemic again when they’re carried to a new region or when conditions change.