The 'Fourth Reich' is a shorthand for the modern day 'Holy Roman Empire' (European Union).
"The Holy Roman Empire (Latin: Sacrum Imperium Romanum; German: Heiliges Römisches Reich), often unofficially referred to as the Holy Roman Empire of the German Nation,[7] was a multi-ethnic complex of territories in Western and Central Europe that developed during the Early Middle Ages and continued until its dissolution in 1806 during the Napoleonic Wars.[8] The largest territory of the empire after 962 was the Kingdom of Germany, ..."
https://en.wikipedia.org/wiki/Holy_Roman_Empire
It was basically a unifying force, similar to the European Union.
So ...
1. There's no 'National Identity' as far as the EU is concerned, they all have their own 'identities'. (which we both agree upon)
2. And, yes, I agree, once you let a large percent of Foreigners into a Nation, you dilute the National Identity. (I think it's a fait accompli, in other words, too late to do anything about it)