After thousands of years of histories, countless cultures, empires, nations, civilizations, etc... people STILL think that the current cultures that exist today will last forever? Is British culture today unique from what it was a century ago? 3 centuries ago? What about when the French ruled for 300 years?
Why be scared by a constant of history? Why not make it easy on everyone in the world and stop fighting (generally peaceful) change and work to make the transition to the future cultures a bit more peaceful? Britain is gaining more middle eastern and Indian ways, but the converse is also true.
man....