Although I agree with almost all of what you say Lizzie, there's one thing that you don't say (forgive me if you have but I've missed it).
That is, the population that is 'invaded' by newcomers at all these points in history were (I speculate!) never very happy about what was happening at the time.
Just because mankind theoretically has the capacity to study and learn from history, to potentially remove the fear aspect by seeing that 'things turned out OK last time', doesn't mean people will think that way. They'll just be afraid and cross, mostly.
Absolutely right, they were not
at the time.

However, within a short space of time the Romans, the Anglo Saxons, the Vikings and the Normans , who caused the biggest changes before the birth of the British Empire, were considered of great benefit to those living in England, and were missed when their power faded.
To cut a long, long story: Leaping forward in time with the coming of the Blacks from former / existing British colonies in the 1950's were not welcomed. But now how we value their descendants who are medical, legal, engineering, scientific, teaching, etc, etc, professionals, and how we could not do without them!
It is especially the English who have NEVER welcomed change, especially if it was not white Christian English, but that did not include Catholics or Protestants at certain periods in our history, and as for the Welsh of Scottish peoples..............well jokes still abound in English circles about those tribes who once were enemies of England but now are really close friends.
We soon get over change, and that drove the Empire and the Industrial Revolution on to achieve really Great things, often with the aid of "foreigners" who found their way to our fair shores.
Finally, I would ask can anyone in this Great Isle really claim a PURE British blood line, with truely British DNA all the way back to the ancient Brits? They are the rarity, not us who are in the huge majority from IMMIGRANT blood and DNA. The mix has been the wonderful factor in British history and has avoided the terrible inter breeding that otherwise would have taken place, as it did in certain sectors of the aristocracy!
