In Doctor Who series 9 the "Cloister War" was mentioned a few times (by Missy in episode 1, and the Doctor in episode 12).
When did this war happen? Was it on a big scale, and who was involved besides the Daleks, Cybermen and Weeping Angels? What were the motives to attack the cloisters on Gallifrey? And why wasn't the war focused on capturing Gallifrey itself? The cloisters are underneath the capital and hard to reach: how did the Daleks and others get there without capturing Gallifrey?