In England, in the absence of census figures, historians propose a range of pre-incident population figures from as high as 7 million to as low as 4 million in 1300,[51] and a post-incident population figure as low as 2 million.[52] By the end of 1350 the Black Death had subsided, but it never really died out in England over the next few hundred years: there were further outbreaks in 1361–62, 1369, 1379–83, 1389–93, and throughout the first half of the 15th century.[53] The plague often killed 10% of a community in less than a year—in the worst epidemics, such as at Norwich in 1579 and Newcastle upon Tyne in 1636, as many as 30 or 40%. The most general outbreaks in Tudor and Stuart England, all coinciding with years of plague in Germany and the Low Countries, seem to have begun in 1498, 1535, 1543, 1563, 1589, 1603, 1625, and 1636.[54]

The plague disease, generally thought to be caused by Yersinia pestis, is enzootic (commonly present) in populations of ground rodents (most specifically, the bobac variety of marmot)[23] in Central Asia, but it is not entirely clear where the 14th-century pandemic started. The popular theory places the first cases in the steppes of Central Asia, although some speculate that it originated around northern India, and others, such as the historian Michael W. Dols, 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 Africa and spread to Central Asia, where it then became entrenched among the rodent population.[24] Nevertheless, from Central Asia it was carried 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 at the trading city of Caffa in the Crimea in 1347. After a protracted siege, during which the Mongol army under Jani Beg was suffering the disease, they catapulted the infected corpses over the city walls to infect the inhabitants. The Genoese traders fled, taking the plague by ship into Sicily and the south of Europe, when it spread.[25] Whether or not this hypothesis is accurate, it is clear that several pre-existing 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.[26] The 14th-century plague is estimated to have killed one third of the population of China.[27]