>>49985904>into one French raceThere is no "French race". France is a Romano-Celto-Germanic clusterfuck of races and -unlike Germany- race never mattered to them.
Why the French managed to do that? Long story short, the revolution. Prior to that the kings were kings of France and Navarre (king of like how the British kings had four kingdoms and the Spanish kings were kings of Castille and Aragon) and at best 25% of the population spoke French. An expression from the eve of the Revollution was: “Federalism and superstition speak Breton, emigration and hatred of the Republic speak German, the counter-revolution speaks Italian and fanaticism speaks Basque.” All of the aforementioned languages as well as Catalan, Occitan, Picard and a few others were big things in France.
The Revolution made power rely on popular sovereignity, as such the people needed to be united to avoid separatism. The Republics and Empires did their best to ensure this by destroying the local languages and cultures and enforcing French on everyone through rather brutal means (for example, French teachers would beat their students with a wooden stick or spoon if they spoke any language but French in school). The French identity was fabricated out of necessity.
Compare Spain, which remained a backwards Ancien Regime shithole until very recently, and by the time it got its shit together society had softened up with teachers no longer being allowed to physically punish students, minority languages having arbitrary rights etc. etc. By the time Spain caught up to France, it was no longer possible to downright eliminate competing cultures.
Had France not done what it had done, we'd see the same shit in Bretagne we're seeing in Catalonia right now and Corsicans would constantly protest in favor of being handed over to Italy and other such nonsense.