The Black Death, also known as the Black Plague, refers to a devastating pandemic that widely affected Europe and western Asia, and North Africa in the middle of the 14th century. Medieval statistics are difficult to estimate with any reliability, but it probably killed between one-third and two-thirds of affected populations. Globally, it is thought that the Black Death killed at least 75 million people. The same disease is thought to have returned to Europe at least every generation with varying degrees of virulence and infectivity until the 1700s.
The exact infection is a subject of dispute, but the dominant opinion is that it was Yersinia pestis, presenting in the bubonic form of plague. "Bubonic" refers to the symptomatic bubo, a swelling of the lymphatic gland. The most common vector of plague is from rat to man via fleas. 
Effects in Europe
The Black Death first struck Europe in the mid-14th century (1347–1351). It may have killed about half the population. In addition to the devastating social effects, it increased the wealth per head of the survivors because domestic animals and other assets were not affected. In many occupations there was a move away from labour-intensive activities to greater use of natrual forces and in agriculture from crop cultivation to animal husbandry.
- "Disease and History," Frederick F. Cartwright in collaboration with Michael D. Biddiss, Dorset Press, 1991, pgs. 29, 30
- Belich, J. The Black Death and European Expansion. The Oxford Historian issue XII 2014/15