The Black Death
In 1348, during the reign of Edward III England was hit by the bubonic plague known as the "Black death" because the body went dark-coloured after death.
It was caused by fleas living on black rats which infested the ships trading with Europe and spread because in the medioval period living condition for rich and poor like were primitive, dirty and unhealthy.
The mortality rate was very high; it is generally thought that the plague killed a third of England's population.
The economic and social effect were great. Labour was scarce, so wagws rose, prices dropped, and the condition of those peasants who survived inproved since they were able to demand payment for work done on the lord's land.