You English turned out OK after the Normans took you over, no? You got a much nicer language, though you also had to deal with Norman oppression for a couple of centuries or so afterwards.
We were pretty good before then. It mean widespread massacres and a huge destruction of resources as well as the transfer of what was left from the home population to the new foreign overlords. To a degree it also caused the class system that still impedes the country today.