There was no real medicine and/or hygiene at the time, so how did the plague come to an end? I know there are some ongoing cases, but why wasn't the plague killing people at the same prevalence as today's flu every year throughout the world until treatment became available?
Heya! I have an earlier answer that might interest you:
It considers the cyclical nature of pestilence reoccurring in late medieval/early modern Europe and the development of better containment methods. I do wish I'd added epidemiologists' speculation that Y. pestis itself evolved--it was too virulent in its late medieval form, killing too many people too quickly for it to become truly endemic. Natural selection eventually ground out a bacterium that was slightly more mild in virulence.