There is no denying that the Roman Empire fell when too many people inside it weren’t “Roman” in any sense of the word - regardless of “citizenship”. The eastern half existed as a shadow of the former greatness of the whole, slowly rotting and shrinking until the Turkish coup de grace in 1453.
For all of their “inferiority”, the barbarian tribes of the north would see a Germanic language become the international language of business today, while the hordes pouring across our southern border speak a tongue descended from the Roman Empire.
Rome fell, or rather the Western Roman Empire fell due to:
Extension of citizenship was continuously done throughout Roman history -- from Alba Longa to the Social Wars (extending citizenship to all of Italy), then to Hispania and Cisalpine Gaul, then under Caracalla to all of the Empire (expanding the tax base)
English might be at its base a Germanic languages, but 70% of its words are French/ Latin/Italian/Spanish in origin. And English grammar follows the French fashion of dropping of cases -- if it was really a Germanic language it would have 5 cases instead of 1 today (Nominative, Genitive, Locative,Dativa,Vocative)
So English IS descended from Latin to a large extent as well as from proto-German (I call it a bastard language :)