Analysis of information sources in references of the Wikipedia article "Viking expansion" in English language version.
Several Viking leaders joined forces in the hope of winning status and independence by conquering England, which then consisted of four kingdoms. In 865 a fleet landed in East Anglia and was later joined by others to form what a contemporary chronicler described, with good reason, as a 'great army'.
The leaders appear to have included Ivar the Boneless and his brother Halfdan, sons of the legendary Ragnar Lothbrok, as well as another 'king' called Bagsecg, and several 'earls'; and if it is assumed that Ivar is the Imar who had been active in Ireland in the late 850s and early 860s, it would appear that he had been able to meet up with his brother and assume joint leadership of the army some time after its arrival in England.
[...] the heathen armies spread devastation among the Northumbrians, and plundered the monastery of King Everth at the mouth of the Wear. There, however, some of their leaders were slain; and some of their ships also were shattered to pieces by the violence of the weather; many of the crew were drowned; and some, who escaped alive to the shore, were soon dispatched at the mouth of the river.
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