Phys.org [phys.org]:
This research indicates that the Vikings were not the worst invaders to land on English shores at that time. That title goes to the Anglo-Saxons, 400 years earlier.
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One support for this contention is the impact, or rather the lack of impact, that the Viking Old Norse had on contemporary Old English language of the Anglo Saxons in the ninth and 10th centuries. This should be compared to the absence of Celtic language in England in the fifth and sixth centuries after the Anglo-Saxons had arrived.In the fifth and sixth centuries, Old English wiped out the earlier Celtic language in a similar way that modern English eradicated the language of the Native Americans in U.S. in the 19th and 20th centuries. This is clear in the almost non-existent impact that Native American words have on the English spoken today in the U.S. Modern American English has retained around 40 Native American words. Similarly, only a dozen Celtic words made it into the Old English of the Anglo Saxons.
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If the Anglo-Saxons eradicated the Celtic language, the Viking's impact was significantly less. Linguists do see some influence from the Old Norse of the Vikings in the Old English language. But it doesn't come close to the eradication of Celtic by the Anglo-Saxons.
Hmm, perhaps, but the Vikings did introduce 900 glorious ways to say, "I smite thee!"