Three Immortals by Bert-Oliver Boehmer
Extra-galactics ravaged the Milky Way and humans saw their interstellar civilization burn. 2400 years later, humanity has risen again. Its immortal rulers are challenged by a ruthless empress. When popular war hero Kel Chaada rises to lead a small nation of mining worlds, his life gets crushed between the clashing powers. Charged with murder, he has to flee human space. At the fringes of the known galaxy he discovers ancient alien civilizations, and the legendary powers they have to share.
Why was their existence purged from the historic records by the immortal elite?