Chris Bunch 
Demon King 
Book Two of the Seer King Trilogy

The thrilling second novel in the epic Seer King trilogy!Ten years ago, General Damastes pledged eternal loyalty to the wizard Tenedos when the seer sought to realize his vision of a peaceful, unified Numantia. Yeteven though Tenedos became the Seer Kingpeace never came. Instead, his enemies were slaughtered and Damastes needs to prepare for war. Now, as the battle dawns upon him, Damastes must question his long-held loyalty and the oath he swore. And he will discover the horrifying bargain Tenedos made to gain an empire and the price that must be paid.