The Mongolian invasion
It was a confrontation between the Holy Roman Empire and the Papacy. Please see the link below.
Dispute between the popes and the Holy Roman Emperors over who held ultimate authority over bishops in imperial lands.
Because on the 11th minute of the 11th hour of the 11th day of the 11th month the Armistice to end the War to End All Wars was signed, bringing an end to the hostilities of...
importance (the quality of being important and worthy of note)