Saga of the Skolian Empire #1: Primary Inversion by Catherine Asaro

The Skolian Empire rules a third of the civilized galaxy through its mastery of faster-than-light communication. But war with the rival empire of the Traders seems imminent, a war that can only lead to slavery for the Skolians or the destruction of both sides. Destructive skirmishes have already occurred. A desperate attempt must be made to avert total disaster.