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