NoteCharles [Charlemagne]'s empire did not survive his death, and its disintegration and eventual resurrection were vastly influenced by two great ethnic upheavals: the coming of the Vikings in the ninth century and of the Magyars in the tenth. The latter were a Ural-Altaic people who in 895 occupied the region of the upper Theiss, and by doing so divided the northern from the southern and the western from the eastern Slavs, and in consequence [between 907 and 955] altered the course of European history. ...

  ² A generic term for the Scandinavian sea rovers of the ninth and tenth centuries; called also Northmen or Norsemen, Danes and Varangians, according to the localities of their operations. the word is derived from "vik", an inlet, creek or bay, and as "wick" is to be found in many English place-names.

      The anarchy following these incursions, coupled with that created by the Vikings and Slavs, resulted in West Frankland reverting to its tribal divisions of Saxony, Bavaria, Franconia, Swabia, and Thuringia, each under its own duke. Although these duchies tended toward becoming separate kingdoms, they could not altogether afford to dispense with a central government. Nevertheless, anarchy continued until 918, when Conrad I (911-918) - then nominal King of Germany - offered the crown to Henry the Fowler (919-936), son of Otto the Illustrious, Duke of Saxony, as the only man able to cope with the prevailing disorder.
      A born soldier and able statesman, Henry subdued Swabia and Bavaria, annexed Lorraine, drove back the Slavs and Magyars, and finally reunited all Germany. On his death in 936, he was succeeded by his son Otto I (396-973), known as the Great, a brother-in-law of King Athelstan of England. He overthrew the Magyars at Lechfeld, near Augsburg, in 955, and next forced the Bohemians, then the strongest Slav state, to pay tribute to him. In 961 he was called to Rome by Pope John XII, who needed his aid. there, on February 2, 962, he was crowned by John, and after the customary courtesies and promises had been exchanged between them, John owned himself his subject, and the citizens of Rome swore that in the future no pontiff would be elected without the Emperor's consent. Thus, by vesting the sovereignty of Germany and Italy in a German prince, the Holy Roman Empire, as it was known in later centuries, came into being. It was a prolongation of the empire of Charles ...
      Before these changes, the Vikings - the wagon-folk of the seas - had swept up the creeks and rivers of western Europe, and though the first of their raids came early in the reign of Charles the Great, it was not until after his death that they grew more and more formidable. In 850 the whole manhood of Scandinavia took to the sea ...
      These incursions, which were carried as far as Novgorod, Sicily, Iceland, Greenland, and America, vastly stimulated the military organization initiated by Charles. As ill-armed levies were useless, professional soldiers became essential, and because mounted men alone could keep pace with the raiders, more and more did military power pass into the hands of the nobility. Thus, out of these troubled times, emerged a completely feudalized society based on the stronghold and the mounted knight. In England alone were other means adopted by King Alfred (871-900); for although he also relied on fortifications, instead of raising cavalry he built a fleet and beat the Vikings on their own element. This led to the English continuing to rely upon infantry, while on the continent cavalry became the dominant arm.
      Of these many incursions, the two most pregnant with future events were those made against England and northern France. Both began with plundering raids, were succeeded by settlements and finally developed into conquests. The former, which began at the end of the ninth century, ended when England was annexed to Denmark under King Cnut (995-1035) to become part of his Scandinavian empire. The latter dates from 896, when a Viking named Rollo or Rolf came to France. For a time he struggled against Charles the Simple (893-929), and in 911, Charles, unable to overcome him, by the treaty of Saint Clair-sur-Epte, agreed to cede to him and his followers the region of the lower Seine on condition that they were baptized, and he himself did homage to him for his lands. Thus was created the Duchy of Normandy, which by 933 extended to the Breton border. Thus also was the stage set for the struggle between Normandy and England.
      In brief, the events which led to this climax were as follows:
      In the year 1002. as some historians suppose, in order to deny the harbours of Normandy as refuges to the Danish invaders, Aethelred II, the Unread (of No-Counsel) or Unready, married Emma, sister of Rollo's great-grandson, Richard II of Normandy. Next, in 1013, during the invasion of England by Swein Forkbeard, King of Denmark, Aethelred, his wife and two sons, Alfred and Edward, fled to Normandy and were kindly received by Richard. A few weeks later Swein died, and when Aethelred returned to England, Cnut, the younger of Swein's two sons, found himself unready to meet him and carried the Danish fleet back to Denmark to recruit fresh forces. In 1015 he returned and within four months of his landing established himself firmly in Wessex. On Aethelred's death, in the following year, the war against the Danes was continued by Edmund Ironside, son of Aethelred by his first wife Aelfgifu. After fighting six battles, in 1016 Edmund was defeated decisively at Ashingdon (Assandun), and came to an agreement with Cnut. By its terms Edmund was to keep Wessex, and the whole of England north of the Thames was to go to Cnut. This settlement was short-lived, for on November 30 Edmund died, and in order to avert a renewal of the war, the West Saxons accepted Cnut as king of all England. Edmund's two young sns, Edmund and Edward, were then banished by Cnut, and to avert assassination they sought refuge [via Poland] in Hungary. The next year, to forestall any action by Richard of Normandy on behalf of his nephews - Aethelred's and Emma's two sons - Cnut entered into treaty with Richard and married Emma.
      Cnut's empire included the kingdoms of England, Denmark, and Norway, and on his death in 1035, like Charles the Great's, it was divided between his three sons. Swein took Norway, Harthacnut Denmark, and Harold, surnamed Harefoot, claimed England. The first and third were Cnut's alleged sons by Aaelfgifu of Northampton, and the second his legitimate son by Emma ; therefore, so far as succession was concerned Harthacnut had a better claim than Harold to the English throne. But there were other candidates in the field who had as good, if not better claim than either - namely, the sons of Edmund Ironside and those of Aethelred and Emma. The former were out of reach in Hungary, and the latter were no longer under the care of the friendly Robert I who had succeeded Richard II in 1028 and who had died in 1035. He had left his duchy in the hands of his son William, later to become known as the Conqueror, but as he was not yet eight years of age, and his duchy was distracted, he was not capable of intervening on behalf of the Aetheling Alfred and his brother.

(Fuller, vol. I., pp. 354-357).