A History of Germany in the Middle Ages

"The fortunes and misfortunes of a Charlemagne and Henry IV., of a Barbarossa, a Henry VI. and an Emperor Frederick II... The rise and fall of the mediæval German Empire is in itself a subject boundlessly interesting, boundlessly important. ...See how Europe has come to be what it is, and how near it came to being something quite different! If Italy had remained under the sway of Germany, if Frederick Barbarossa or his successors had done away with the papal power, as they often seemed about to do, would the fate of England and France have been the same?"

Ernest F. Henderson