Crusade

Crusade, by James Lowder, is the final book in The Empires trilogy.

"Yamun Khahan and his mighty barbarian army have turned their sights on the civilized western nations of the Forgotten Realms. Only one man, King Azoun of Cormyr, has the courage and the strength to bring the western factions together and forge a crusading army powerful enough to challenge the Tuigan horsemen. Together with the dwarves of the Earthfast Mountains, the crusaders make their stand against the rampaging horde. But King Azoun hasn't reckoned that the price of saving the west might be high—perhaps even the life of his beloved daughter."