Branegate — James C. Glass

The Immortals created a passage from one universe to another and founded peaceful colonies there, but now the homeworld is ruled by a corrupt council that will send an army to put the colonies under harsh rule. On the colony world of Gan, Trae is raised in secret by a religious sect hiding from a crazed emperor. The reincarnated son of an immortal prophet, Trae is guided by a mentor mysteriously connected to his father, is raised to lead a revolution against the Emperor and, reunited with his true family, moves to meet the threat of the conquering horde streaming in from another universe.