Cloister Wars
From Tardis Wiki, the free Doctor Who reference
The Cloister Wars were an amount of conflicts that had happened long time ago, presumably on Gallifrey, mentioned by Missy to Clara Oswald along with a night he stole the moon and the President's wife and since he was a little girl when explaining how long she had cared for the Doctor, and asked her if she could distinguish the lie. (TV: The Magician's Apprentice)