The Black Death was a plague pandemic that occurred in Europe from 1346 to 1353. It was one of the most fatal pandemics in human history; as many as 50 million people died, perhaps 50% of Europe's 14th-century population. The disease is caused by the bacterium Yersinia pestis and is spread by fleas and through the air. One of the most significant events in European history, the Black Death had far-reaching population, economic, and cultural effects. It was the beginning of the second plague pandemic. The plague created religious, social, and economic upheavals, with profound effects on the course of European history.