The Telepath War was a conflict between non-telepathic humans and the Psi Corps.
During the war the Psi Corps attempted to take over the Earth Alliance. During the war the Interstellar Alliance entered the fight to help on the side of the humans and rogue telepaths.
Following the war, the Psi Corps was disbanded, and the Psionic Monitoring Commission was created.
Notes
The exact dates of the war are not given, but it was "recently" over by the time of "A Call to Arms," set in 2267.