Great War (The Library in the Body)

The Great War was a devastating time war in a Parallel universe. During the war, reality broke and whole civilisations were burned out of time.

The Doctor told Bernice Summerfield that he had tried to help from the sidelines, but there was no way to stop the devastation (or if there was, he had forgotten it in the shifting of the timelines). However, Mandeville claimed that the Doctor had been a main participant, called the "cautious warrior" for his strategy of sidling up to his enemies and cowardly stabbing them in the back.

The war ended when the combatants ran out of weapons and galaxies. None of the survivors could remember what it was about. Since everyone before him in the line of succession had been killed, the Doctor was left as Ruler of the Universe. (AUDIO: The Library in the Body)