Janet L. Nelson 
Charles The Bald [PDF ebook] 

This important and long-awaited study is the first full-scale biography of Charlemagne’s grandson, King of the West Franks from 843 to 877, and Emperor from 875. Posterity has not been kind to Charles or his age, seeing him as a fatally weak ruler in decadent times, threatened by Viking invaders and overmighty subjects. Janet Nelson, however, reveals an able and resourceful ruler who, under challenging conditions, maintained and enhanced royal authority, and held together the kingdom that, outlasting the Carolingians themselves, in due course became France.