the Black Plague or Yersinia pestis and wiped out roughly 30% to 60% of the continent's entire population.

 The Continent being Europe. Imagine if something like the Hantavirus became mobile like the Black Plague did and wiped out half of Europe and half of the Americas population wise.

Of course with Trump as president this could actually happen because his government is the most likely to let something like this happen worldwide because it is the most incompetent government I have seen in my lifetime both Republican and Democratic since 1950 which is as far back as I can remember now as a 78 year old.