Because one of the peripheral kingdoms that rise up in the wreckage of the empire is overtaken by a rogue - a ruler who can telepathically alter the minds and loyalties of people he comes into contact with.
2
Professor X's first student was 11-year-old Jean Gray, traumatized when she telepathically experienced the emotions of a dying friend.
3
They are paired with horse-like creatures, called Companions, who can communicate with them telepathically.