The Sky-Blue Wolves (Emberverse #15)

Many years ago, when advanced technology failed and humanity found itself in a turbulent, postapocalyptic world, extraordinary men and women birthed a new society from the ashes. In this new world of emperors and kings, new leaders emerged, making the world their own.

Two generations after the Change, Crown Princess Órlaith struggles to preserve the hard-won peace her father brought to Montival--the former western United States. But the Change opened many doors, and through them powers strong and strange and terrible walk once more among humankind.

With her fire-forged friend and ally, Japanese Empress Reiko, Órlaith must take up her sword to stop the spread of the mad malignancy behind the Yellow Raja, who has imprisoned her brother Prince John. And from the emerging superpower of Mongolia, the Sky-Blue Wolves of the High Steppe ride once more beneath the banner of Genghis Khan--the thunder of their hooves resounding across a world in turmoil.