The Emperor used some of the last vestiges of his psychic powers to cause a storm, sufficient to save them. Since the Tau do not have psychic powers, their presence in the Warp is null, causing the powers of Chaos to ignore them, like a scentless fish in a sea of blind sharks. By being only shadows cast on the backdrop of the Warp, Chaos ignored them, but the Emperor realized their potential. Meanwhile, Eldar Farseers used their ability to see into the future to realize the Tau's potential and created the Ethereals using an alien hormone to influence their decisions. While unable to directly control the Tau, the Eldar could now ensure their development into a galactic power and thus see their potential as a future ally against Chaos realized.