I've seen a couple of videos from respectable sources that downplay the idea that there was an Anglo-Saxon invasion of Britain after the Romans left.
- https://youtu.be/glKe9njOB24 "Roman Britain - The Work of Giants Crumbled" from the wonderful "Fall of Civilization Podcast" by Paul MM Cooper.
- https://youtu.be/OyCHtdpymNw "Is The Anglo-Saxon Invasion Of England A Myth?" from archeologist Francis Pryor.
I also watched a video about the infamous 536 AD volcanic eruption, which produced the worst year in history in Europe: https://youtu.be/HOw9UlRpfSA "The Mystery Volcanic Eruption in 536; The Year of Hell". This is from the excellent GeologyHub. There were 2 big eruptions close together. The 536AD one was probably in Iceland or Alaska and mostly affected the Northern Hemisphere. The 540AD one was even bigger, coming from near Krakatau (aka Krakatoa). It affected the whole world, but merely added to the misery in Europe.
Ship building and sailing expertise was improving rapidly in the centuries on either side of 410AD when the Romans left Britain. The North Sea was a highway, linking navigable rivers on both sides. So in 410 there were already plenty of people from across the North Sea enjoying the Pax Romana in Britain, and the work opportunities it provided, such as in the army.
The change when the Romans left was that land travel in Britain became less safe and less efficient. Travel by boat was the glue that linked parts of Britain together, but also linked Britain, particularly the East coast, to the people of North-West Europe.
After 410, trade was by boat, and the traders were from those Germanic people in NW Europe. They didn't speak Latin or the British languages. They probably all grew up speaking local languages, but a trade network like that develops a common language, just as bahasa Indonesia developed across Indonesia. That language became a natural lingua franca in England as well. Everybody had to learn it to trade, and it then facilitated communication with other people in England. And it was a prestige language. No wonder it took off, replacing Latin as "the language everyone knew".
Then 536-7 hit, and a little bit later 540. The weakened population was susceptible to the Plague of Justinian that then followed. It is almost certain that Britain was substantially depopulated. The people who had a big advantage in surviving were those who could turn to the sea for food. These were the people around the coast who were most influenced by the "Anglo-Saxon" ship traders. Surviving people then came together in communities that were more mixed, and were even more inclined to take up the common language and other culture of the wealthy traders.
The North Sea was a connected world that Britain was a part of. The connection is still apparent. As the Frisians say: "Good butter and good cheese is good English and good Frieze".
Update 2024-11-05:
A recent video suggest that England was substantially German/Scandinavian before the Roman invasion: https://youtu.be/XG9gWjSxK4g?si=5xaFGDiWze4_bazH. This makes so much sense. I've put a transcript of the relevant bit below, but I recommend the whole video.
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For instance, there's a near complete absence
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of celtic inscriptions in England outside Cornwall,
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while such inscriptions are common in Ireland,
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Wales, Scotland and Brittany.
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So who were the Britons living in England
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at the time of the roman invasion?
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The history of pre roman coins in southern
13:33
Britain points to strong connections with belgic Gaul.
13:37
In fact, many of the tribes living
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south and along the southern coast during
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Caesar's time had belgic names or affiliations.
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Caesar himself noted that these large belgic
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settlements had replaced an earlier british population
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which had retreated inland, possibly including the
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large celtic tribe known as the Catuvellauni.
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The roman historian Tacitus also remarked that the
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languages of Britain and Gaul were quite similar.
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However, the common language Tacitus referred
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to may not have been celtic.
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It's possible that the language spoken by the
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Belgae in southern England was more germanic as
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Caesar suggested, this hints that a germanic type
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language might have already been spoken in England
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before the roman invasion.
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Recent research by Cambridge geneticist Peter Forster and
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colleagues supports this idea, showing that the split
14:36
between Old English and continental germanic languages occurred
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much earlier than the dark ages, suggesting that
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English could have been a distinct branch of
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the germanic language family before the Romans arrived.
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Besides the belgic presence in the south, genetic
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evidence also shows significant scandinavian incursions into northern
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and eastern Britain, from Shetland to Anglia during
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the neolithic period, long before the Romans.
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These findings align with the strong
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cultural exchanges across the North Sea
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during the neolithic and Bronze Age.
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Early anglian dialects, such as those found
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in the old English epic Beowulf, owe
15:19
much of their vocabulary to scandinavian languages.
