Channel's Destiny by Jean Lorrah, Jacqueline Lichtenberg
The world of the Simes and Gens is teetering on the brink. Zeth Farris reaches adulthood just when things start to fall apart. When he finally understands the audacity of the social engineering experiment that his parents have set in motion, Zeth must build bridges with potential allies to hold the center together. But war comes anyway, and Zeth and his alliance must prevail. The price of failure?--the destruction of his family, his culture, even his world! Sime~Gen, Book Five.