Great Schism
From Tardis Wiki, the free Doctor Who reference
The Great Schism was an event that befell the planet Gallifrey long before the Gallifreyans took their position as Time Lords. It involved a war between the forces loyal to Rassilon and the female priesthood of the Pythia. The ruling matriarchy was defeated and banished from Gallifrey, but not before the Pythia cursed the Gallifreyans with sterility. This led to a change in their reproduction. Because their women could not longer give birth, the Looms were created. (PROSE: Lungbarrow)
