Oathbreakers: The War of Brothers That Shattered an Empire and Made Medieval EuropeThe authors of The Bright Ages return with a real life Game of Thrones the story of the Carolingian Civil War, a bloody, protracted battle pitting brother against brother, father against son, that would end an empire, upend a continent, and redefine the future of Europe By the early ninth century, the Carolingian empire was at the height of its power. The Franks, led by Charlemagne, had built the largest European domain since Rome in its heyday.