Answer:
The plague - The death toll was so high that it had significant consequences on European medieval society as a whole, with a shortage of farmers resulting in demands for an end to serfdom, a general questioning of authority and rebellions, and the entire abandonment of many towns and villages. Throughout history, there have been many deadly pandemics, but the Black Death and the influenza pandemic of 1918–19 rank among the most lethal. The Black Death, which ravaged Europe between 1347 and 1351 and likely was caused by plague, killed roughly 25 million people.
Magna carta - Magna Carta was issued in June 1215 and was the first document to put into writing the principle that the king and his government was not above the law. It sought to prevent the king from exploiting his power, and placed limits of royal authority by establishing law as a power in itself.
Thus, the Magna Carta that is commonly remembered is the Magna Carta of King John, and the date that always has been commemorated as its granting is 1215.