Stamford Bridge fella's is all you need to know

Then you put down your swords to settle here instead cos you were so tired of having to keep coming back to try to keep the anglo-saxons down, just in time to get spanked along with the anglo-saxons by a load of randy normans.

The real peoples of the British Isles you did not fight because they lived in areas too harsh for you to go, anyone can take people off guard.
No-one has ever invaded those area's apart from the romans and that proved to lead towards their downfall.