Edmund was only eighteen years of age when, in A.D. 940, he succeeded to the crown of his brother, whose activity and vigour had secured to England for a few years before his death a profound repose. The Welsh paid their tribute with the utmost regularity; the Danes, who had so frequently experienced his prowess, desired no better than to remain at peace; and the unfortunate Anlaff, who, after the defeat of his hopes, had once more retired to Ireland during the reign of his conqueror, did not renew his attempts.
No sooner was it known, however, that Athelstan was dead, and a mere youth upon the throne, than the Danes prepared to revolt. Several years of fighting followed, but the accounts are so conflicting that it is almost impossible to harmonise them. According to one version, Anlaff, who was informed of all that passed, deemed that the time was come for the prosecution of his claims, and entered into a treaty with Olaf, King of Norway, for assistance, which being liberally granted, he once more appeared in his father's kingdom of Northumbria, and obtained possession of York, the inhabitants opening the gates to him.
This example being followed by most of the neighbouring towns, the long-exiled prince soon found himself in a position to carry the war into Mercia, where his countrymen received him as a deliverer, and by their united efforts many strong places were recovered which Edward had taken from them.
Edmund, though both young and inexperienced, appears to have inherited the courage of his race. The success of the enemy, instead of depressing him, rendered him more eager for battle; he marched at once to the north, and Anlaff, with equal confidence, advanced to meet him.
A battle was fought between these rival princes near Chester, in which success was so equally balanced, that it was impossible to say on which side it preponderated. Then, according to the chronicler Simeon, the Archbishops of York and Canterbury, to avoid any further effusion of blood, prevailed upon the parties to make peace. Anlaff was permitted to retain possession of the kingdom of Northumbria, and the whole country north of Watling Street.
The Northumbrians had not reason long to rejoice at the restoration of Anlaff, which they had so ardently desired; for this prince, having contracted a large debt with the King of Norway for the troops he had lent him, was anxious to pay it; and to this end laid heavy taxes on the people, by which he forfeited their affection. The inhabitants of the ancient kingdom of Deira were the first that revolted, and having sent for Reginald, his brother Godfrid's son, crowned him king at York.
Reginald was no sooner on the throne, than he armed against his uncle, who was also preparing to dispossess him. The quarrel between these two kings incited Edmund to march towards the north at the head of an army, to appease the troubles there, being apprehensive they might give occasion to the foreign Danes to return into England. He arrived upon the borders of Northumbria, when the uncle and nephew, wholly intent upon their private quarrel, thought of nothing less than repulsing the English. He probably might with ease have made himself master of that kingdom; but he was contented with procuring peace between the two kings, in such a manner that Reginald was to keep the crown he had lately received; but at the same time, Edmund obliged them both to swear allegiance to him, and be baptised, himself standing godfather.
This forced peace did not last long, and Edmund had hardly returned into Wessex, when the two Danish princes took up arms to free themselves from his yoke, having engaged the Mercian Danes and the King of Cumberland to espouse their quarrel. Whereupon Edmund immediately marched into Mercia, and before the Danes there could be joined by the Northumbrians, took from them the five boroughs, i.e. Leicester, Stamford, Derby, Nottingham, and Lincoln; and then, advancing with the same expedition towards Northumbria, he surprised the two kings before they had drawn their forces together. This sudden attack threw the Northumbrians into such disorder, that their rulers, fearing to fall into the hands of Edmund, believed it their only refuge to abandon the island, where they could not possibly remain in safety, so closely were they pursued; and as their flight deprived the Danes of all hope of withstanding Edmund, they threw down their arms, and gave him allegiance. According to other accounts, the attack upon the Mercian Danes is placed earlier in the reign.
Before he returned to Wessex, Edmund resolved to punish the King of Cumberland, who, without cause, had taken part with the Danes; and he easily subdued that petty kingdom, whose forces bore no proportion to his own, and presented it to the King of Scotland, in order to attach him to his interest, and prevent him from again assisting the Northumbrians; reserving, however, the sovereignty of it, and obliging that king to do him homage, and appear at the court of England at the time of the solemn festivals, if summoned.
Edmund was not wholly employed in military affairs; and some of his laws still exist which demonstrate how desirous he was of the people's welfare and happiness. Having observed that pecuniary punishments were not sufficient to put a stop to robberies, which were generally committed by people who had nothing to lose, he ordered that, in gangs of robbers, the oldest of them should be condemned to be hanged.