Why, when it comes to identity politics regarding European heritage, it is thesis, antithesis… but never synthesis?
That is to say, people are either romanticising the conquerors - for example, Franks/Lombards/Saxons - or romanticising the ‘indigenous’ peoples - for example Gaels/Gauls/Illyrians, with either one or the other being their personal mythos.
It’s always a personal chauvinism. It’s always based around what you perceive yourself to be, which is an ego-driven thought that you then project on to thousands of years of history and square miles. All about what you are the ‘heir’ to, your ‘birthright’, importantly, what sets you apart from others - regionally, nationally, physically.
This trend got more corrosive when applied internationally - when the heirs to Ancient Greece weren’t the contemporary Greeks, but the Germans, with the Germans insisting that contemporary Greeks had no relation to ancient ones. A trend that culminated with the ideology of the ‘Aryan’, the great Indo-European conquerors that swept through - achieved due to genetic superiority - everywhere from Italy to India [again, who the Germans happened to be the sole heirs to].
France isn’t Frankish nor Gaulish in national character, the Franks and the Gauls became, over time, one. Synthesis. The Saxons, Danes, and Brythonic peoples, over time, became one. Synthesis. The Iberians, Celts, Visigoths, and Maghrebs, over time, became one. Synthesis.
None of this has to do with a synthesis of genetics, but a synthesis of culture. Race, as it has been said time and time again, is a modern construct. What divided a Dane and a Saxon was culture, the cosmetic differences were, at best, indicators of culture, not of race [that is to say, there was no race theory attached to a Dane’s blue eyes and a Saxon’s brown. Xenophobia, yes, but not racism. A fear of another group, identified at a glance by certain characteristics, not a pseudo-scientific analysis on superiority and inferiority]
In some cases, an invasion would lead to a change in ruling-class, but not make any real change to the lower classes [Norman England]. With migrations, it could be the case that it changed the lower classes, but not the ruling-class [Visigothic Gaul as part of the Roman Empire]. Sometimes the invaders took on the culture of the lower classes [as consistently happened in Ancient Egypt], and sometimes the lower classes took on the culture of the ruling-class [the Hellenistic world of Alexander, as well as with the Turkic invasion of Anatolia]. These were never absolutes, however, one would never wholly adopt the other’s culture, it would be, as said, a synthesis [with one adding more than the other]. They’d meet, and something new would be born. All cultures are syncretic.
The idea that culture is something material inside people [aka, your 'blood’] is the core of romanticism when it comes to European heritage, and it is false. These identities that we parade as Celts or Gauls or Saxons or Illyrians are, today, absurdities. They’re 19th century romantic concoctions, and their only use is as the tools of ethno-chauvinism, whether recognised as such or not.