From Caffa to the jungles of Vietnam,* war has also been an important predisposing factor in human plague. War creates human remains and refuse, which attract rats; filthy bodies, which attract fleas; and stresses, which can lower immune system function. Marching soldiers and cavalry also help to make a pestilence more mobile. The historical evidence suggests that the existence of only a few of these conditions is not enough to ignite a pandemic, or major outbreak of plague.
