The main cause of the Black Death, which devastated Europe from 1347 to 1351, was the bacterium Yersinia pestis, transmitted by fleas from rats. The plague spread rapidly through trade routes, exacerbated by poor sanitation and crowded living conditions in urban areas. The outbreak led to the death of an estimated one-third of Europe's population. The Black Death had far-reaching social, economic, and cultural impacts, leading to labor shortages, a decline in feudalism, and changes in societal attitudes towards health and religion. It reshaped Europe's demographic structure and prompted changes in medical practices and public health awareness.