In 1204, the great Angevin Empire created by the joining of the dynasties of Henry II of England and his queen, Eleanor of Aquitaine, was fragmenting. At its height, the family landholdings had been among the largest the world had ever seen. From the border of England and Scotland in the north to south of the Pyrenees, it seemed there was nowhere in Europe destined to escape Plantagenet control.
Yet within five years of his accession, King...