I doubt you could say France was that diverse, nor England or Poland.  The superpowers were so also because of geographical and historical coincidence, not necessarily because of their diverse populations.  The USSR was not diverse out of a love of multiculturalism, but Stalin's imperialist ambitions.   And let's not forget the numerous Jewish people we did not accept in our "diverse" and welcome nations before patting ourselves on the back for letting in the few we felt were useful.  So we should be careful before trying to draw analogies from history.  Not that simplistic...