Black Death

In total, the plague reduced the world population from an estimated 450 million down to 350–375 million in the 14th century. The world population as a whole did not recover to pre-plague levels until the 17th century.[8]

.. The plague created a series of religious, social, and economic upheavals, which had profound effects on the course of European history.

.. Because 14th-century healers were at a loss to explain the cause, Europeans turned to astrological forces, earthquakes, and the poisoning of wells by Jews as possible reasons for the plague’s emergence.[11] The governments of Europe had no apparent response to the crisis because no one knew its cause or how it spread. The mechanism of infection and transmission of diseases was little understood in the 14th century; many people believed only God’s anger could produce such horrific displays.