As noted in Dune, Wallach IX is the "ninth planet of Laoujin, site of the Mother School of the Bene Gesserit." Five thousand years later in Heretics of Dune, the primary base of operations for the Bene Gesserit has been moved to a planet called Chapterhouse. The subsequent novel Chapterhouse: Dune notes that the antagonistic Honored Matres have captured Wallach.
In the Legends of Dune prequel trilogy, Wallach is one of the Synchronized Worlds under thinking machine control. It is subsequently devastated by atomics as the human forces of Butlerian Jihad systematically destroy all of the machine-controlled planets. At some point within the next 10,000 years before the events of Dune, the Bene Gesserit assume control of the planet.
Read more about this topic: List Of Dune Planets