What were some of the factors that allowed the Black Death to spreac so quickly and with such deadly results?

Climate changes, rats and flees, poor living conditions, poisoned food were the main factors that allowed the Black Death to spread so quickly.

Black Death or the Bubonic plague was a fatal epidemic that killed a large population. It was considered to be caused by flees and rats. This plague spread very quickly because people of the infected area did not have any knowledge of how to throw waste properly.