The Black Death (also called the "plague" or the "pestilence", the bacteria that causes it is Yersinia Pestis) was a devastating pandemic causing the death of over one-third of Europe's population in its major wave of 1348-1349. Yersinia Pestis had two major strains: the first, the Bubonic form, was carried by fleas on rodents and caused swelling of the lymph nodes, or "buboes", and lesions under the skin, with a fifty-percent mortality rate; the second, the pneumonic form, was airborne after the bacteria had mutated and caused fluids to build up in the lungs and other areas, causing suffocation and a seventy-percent mortality rate.

Modern scholars suggest an array of causes for the Black Death. Some cite Malthusian theory by arguing that the disease was a natural result of the overwhelming population increase in the two centuries...