The Modern Era Has More Large Cities Than the Middle Ages Did

The modern era has seen more severe outbreaks of deadly disease than the middle ages did. It's not because they had better hygiene or medicine in the middle ages, but it's because of just how concentrated the population is. And the middle ages didn't have a lot of large cities. The worst outbreak of plague that ever happened, for example, in london, actually was in 16 66 and called the great visitation.