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.
Probably this prince would have rendered his people happy, had his reign been longer; but a fatal accident robbed him of his life. On May 26th, 946, as he was solemnising a festival at Pucklechurch, in Gloucestershire, Liofa, a notorious robber, though banished the kingdom for his crimes, had the effrontery to enter and seat himself at one of the tables in the hall where the king was at dinner. Edmund, enraged at his insolence, commanded him to be apprehended; but perceiving he was drawing his dagger to defend himself, leaped up in fury, and, catching hold of him by the hair, threw him on the ground. Liofa stabbed him in the breast with his dagger, and the King immediately expired upon the body of his murderer. Thus died Edmund in 946, in the twenty-fourth year of his age, and the sixth of his reign. By Elgiva, his wife, he had two sons, Edwy and Edgar, who did not succeed him, on account of their minority; Edred, his brother, being placed on the throne by the unanimous election of the Witena-gemot. His glorious deeds had deservedly gained for Edmund the title of "Magnificent."