Alright, so the first known major outbreak of the bubonic plague was during the reign of Justinian during the sixth century. What would the consequences on modern history be had the plague simply not happened (the bacteria never mutated into the correct form, or it killed off all of its hosts too soon, or whatever)? I think that the Byzantine Empire and Persia would probably be able to stay at their heights of power (although it still might collapse at some point), meaning that Islam, if it develops at all, would have more difficulty spreading in the way it did in OTL (since its early military victories might be prevented by Byzantine- or Persian-back soldiers). Any other thoughts?