Horselords

Horselords, by David Cook, is the first book in The Empires trilogy. "Between the valiant kingdoms of the western Realms and the exotic eastern lands of Kara-Tur lies a vast, unexplored kingdom. For centuries, the "civilized" peoples of the Forgotten Realms have given little notice to these barbarians. Now, a powerful leader has united the wild horsemen into a mighty force - an army powerful enough to challenge the world."