Ayinde, M. H.. Invoker trilogy #1

"The people of Nine Lands know their history. The kingdom once belonged to the Scathed people, until their greyblood servants rose up and slaughtered them. King Ahiki and his warlords laid claim to the realm by defeating the rebels and driving them out to the Feverlands. Now, thousands of years later, attacks by the greybloods are rebuffed by the invoker clans, warriors of noble blood who summon their ancestors to fight with them in battle. But the war has gone on too long. A general draft is called to take the battle to the Feverlands and defeat the greybloods once and for all. A plan that seems doomed to fail. When Temi, a commoner, accidentally invokes a powerful spirit, she believes it could be the key to ending the centuries-long war. But not everything that can be invoked is an ancestor, and some of the spirits that can be drawn from the ancestral realm are more dangerous than anyone can imagine." --