Black Death migration
The Black Death was one of the most devastating pandemics in human history, resulting in the deaths of an estimated 75 to 200 million people in Eurasia, and peaking in Eurasia from 1321 to 1353. Its migration followed the sea and land trading routes of the medieval world. This migration has been studied for centuries as an example of how the spread of contagious diseases is impacted by human society and economics. Plague is caused by Yersinia pestis, and is enzootic (commonly present) in populations of ground rodents in Central Asia. While initial phylogenetic studies suggested that the plague bacillus evolved 2,000 years ago near China, specifically in the Tian Shan mountains on the border between modern-day China and Kyrgyzstan, this view has been contested by recent molecular studies which have indicated that the plague was present in Scandinavia 3,000 years earlier. Likewise, the immediate origins of the Black Death are also uncertain. The pandemic has often been assumed to have started in China, but lack of physical and specific textual evidence for it in 14th century China has resulted in continued disputes on the origin to this day. Other theories of origin place the first cases in the steppes of Central Asia or the Near East. Historians Michael W. Dols and Ole Benedictow argue that the historical evidence concerning epidemics in the Mediterranean and specifically the Plague of Justinian point to a probability that the Black Death originated in Central Asia, where it then became entrenched among the rodent population. According to eastern origin theories, it has been assumed that the plague transferred from Central Asia east and west along the Silk Road, by Mongol armies and traders making use of the opportunities of free passage within the Mongol Empire offered by the Pax Mongolica. It was reportedly first introduced to Europe when Mongols lobbed plague-infected corpses during the siege of Caffa in the Crimea in 1347. The Genoese traders fled, bringing the plague by ship into Sicily and Southern Europe, whence it spread. However even the Silk Road spread theory is disputed, as others point out that the Pax Mongolica had already broken down by 1325, when Western and Persian traders found it difficult to conduct trade in the region, and impossible by 1340. Preexisting conditions Regardless of its origin, it is clear that several preexisting conditions such as war, famine, and weather contributed to the severity of the Black Death. In China, the 13th-century Mongol conquest disrupted farming and trading, and led to widespread famine. The population dropped from approximately 120 to 60 million. In Northern Europe, new technological innovations such as the heavy plough and the three-field system were not as effective in clearing new fields for harvest as they were in the Mediterranean because the north had poor, clay-like soil. Food shortages and skyrocketing prices were a fact of life for as much as a century before the plague. Wheat, oats, hay, and consequently livestock, were all in short supply, and their scarcity resulted in