Cloister Wars
From Tardis Wiki, the free Doctor Who reference
The Cloister Wars were a series of conflicts mentioned by Missy to Clara Oswald when explaining how long she had cared for the Doctor. (TV: The Magician's Apprentice) While in the Cloister, the Twelfth Doctor encountered a trapped Dalek and hypothesised that it may have been there since the Cloister Wars. (TV: Hell Bent)
