The Basilicom Schism in Hyperdimension Neptunia, is a great war raged on Leanbox ten years ago and was the parliaments revolution. At the time, the Parliament tried to gain total control by gathering heretics in an attempt to raid the Basilicoms. The Aristocrats defeated them under the aegis of the Sanctuary. The heretics escaped, but goddess gave them honor. However, the current Archbishop of the Sanctuary, Yvoire, didn't wish to admit that there was any kind of revolution at all. He burnt all the records and prohibited publicizing any information on it. He even tried to revoke the leader of the Aristocrats' honor.
The reason behind this is because the Parliament fought so the heretics could leave for Lowee, away from the Sanctuary's oppression. The Basilicom concealed this. Aristocrats gained honor by suppressing the Parliament and the Sanctuary gained power. The reason the Archbishop tried so hard to keep the truth hidden is not because he denies the revolt occurred, but rather he didn't want anyone finding out her used the Aristocrats to suppress the very revolt his actions helped instigate. He was afraid to take the blame for oppressing the heretics.