As a result of the black death in western Europe:

While it is not known for certain how many people died, it is estimated that about 25 million people died in Europe from the plague during the Black Death. The Black Death is widely believed to have been the result of plague, caused by infection with the bacterium Yersinia pestis.

It resulted in deaths of millions ranging from 75-200 million people. About 30% of Europe's population.