What was causing people to leave Sandwich?

Due to the Black Plague an extremely devastating pandemic of Bubonic plague that was peaking during the exact same era throughout all of Europe. The mortality rate was extremely high and it would end up killing a third of the population of Europe.

Explanation:

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).