Is very possible that the Saxons migration from around 300 AD, to Britain, was triggered by the raids of Danish Vikings against North Germans.
The Saxons that remained in Germany started to attack later the Danish Vikings to protect Holy Roman Empire.
Otto I, the king of Holy Roman Empire/Germany was of Saxon ancestry.
https://books.google.ro/books?id=rDw...0saxon&f=false

It is quite clear that Saxons have spoken a West Germanic language and were Germans and it seems their relations with the Vikings were not good.
Because is also known that Danish Vikings went to attack the land ruled by Saxons from England.
So it seems that the Danish Vikings and the Saxons were enemies.
There are recorded Danish Vikings raids in Germany, in the 8th century, so just after the Danish wall was built.
https://en.wikipedia.org/wiki/Viking..._the_Rhineland
As a small paranthesis, the rulers of Francia were also German people, but from the Frankish tribes.