The English class system is anchored in this event - the ruling/upper class was replaced in its entirety by the Norman invaders, leaving two very distinct identities.

A reporter for the Financial Times once asked Gerald Cavendish Grosvenor, Duke of Westminster, what advice he would give to a young entrepreneur wanting to succeed. He joked: "Make sure they have an ancestor who was a very close friend of William the Conqueror."

Didn't an existing class hierarchy (at least in part) enable the Normans to do this? When the aristocratic army was defeated, the entire country was defenceless and they could replace the existing aristocracy.