Hello,

(This is my first post on the subreddit, I am currently studying my M.A. on things medieval Scandinavian. So let me know if I'm doing this correctly!)

This is certainly not the case. The first raids which were concentrated around the British Isles were mostly places of worship, Lindisfarne in 793, Jarrow in 796 (which is just some distance south of Lindisfarne), Iona off the west coast of Scotland 3 times in 795, 802, and 806. More were at Howth, Ireland, in 821, and Bangor in 824.

Like allak mentioned, these are soft targets rich in valuable goods. The first notable raids took place in the northern British Isles and were far removed from a realm where Charlemagne's conquest of Saxony would have any relevance. There is nothing in our sources to indicate any particular hatred toward Christianity embedded in a 'revenge' for the period. Even when raids became larger, more organized, and occurred more generally over Western Europe (and even into the Mediterranean), raiding parties had a tendency to avoid engagements where the odds of victory were not overwhelming. This is simply the economics of the matter. To quote Winroth on the matter:

Vikings are often in modern popular culture portrayed as warriors who were violent for the sake of violence itself, but for the Vikings, violence was the calculated means toward desirable ends. In this, they are not different from most political actors in world history.

Anders Winroth, The Conversion of Scandinavia: Vikings, Merchants, and Missionaries in the Remaking of Northern Europe, pg 33.

Ferguson's idea is pretty hard to believe. Frankly when I heard about this (and tracked it down) I was flabbergasted. There are a whole raft of issues with this idea.

It is predicated on a completely anachronistic and non realistic conception of pagan religion, you can find lots of discussion of this elsewhere. At its most basic though, Norse paganism wasn't an organized church, it was a series of different beliefs and practices across a shared cultural continuity.

There is certainly a connection between the growth of Viking activity and Carolingian activity in Saxony but it has little to do with "religion" and far more to do with increased knowledge of and interaction with the world beyond Scandinavia.

After all, why would the Vikings attack the British Isles in revenge for actions taken by the Franks, a people they were in active contact with. They could (and obviously later did) easily attack Frankish sites.

There are already some good ideas presented by others here here, so I am really only going to add some sources and throw in a link to this post Did the Vikings regard Christians negatively and my comment there, which expands a bit on this question.

A few articles worth consulting. All of these look at the question of both how Christians presented/viewed Viking attacks and the probably reality of the Viking's interest in or knowledge of Christianity.

Foot, Sarah. “Violence against Christians? The Vikings and the Church in Ninth-Century England.” Medieval History 1, no. 3 (1991): 3–16.

Lund, Niels. “Allies of God or Man: The Viking Expansion in a European Perspective.” Viator 20 (1989): 45–59.

Coupland, Simon. “Raiders, Traders, Worshippers and Settlers: The Continental Perspective.” In Silver Economies, Monetisation and Society in Scandinavia, AD 800-1100, edited by James Graham-Campbell, Søren Sindbæk, and Gareth Williams, 113–32. Denmark: Aarhus University Press, 2011.

Coupland, Simon. “The Rod of God’s Wrath or the People of God’s Wrath? The Carolingian Theory of the Viking Invasions.” Journal of Ecclesiastical History 42, no. 4 (1991): 535–54.

Coupland, Simon. “The Vikings on the Continent in Myth and History.” History 88, no. 290 (2003): 186–203.