I don't know what it is, but even when I was a kid back in the 80s-90s. It was common knowledge that the vikings who raided Britain where Danes (Danish) not Norwegian. Norway wasn't even a country until several hundred years later. Sure, Norwegian tribes had business with the Danes, and they also fought against each other, just like they united against someone from time to time.
Just take the Ransom the Brits had to pay, it was called Danegeld (Danegæld) "Danish tax", literally "Dane yield" or tribute) was a tax raised to pay tribute or protection money to the Viking raiders to save a land from being ravaged. It was called the geld or gafol in eleventh-century sources. It was characteristic of royal policy in both England and Francia during the ninth through eleventh centuries, collected both as tributary, to buy off the attackers, and as stipendiary, to pay the defensive forces. In Anglo-Saxon England tribute payments to the Danes was known as gafol and the levy raised to support the standing army, for the defence of the realm, was known as heregeld (army-tax).
