I tend to think that old countries retain some trappings of their old cultural identities even though there is a unified government.
If you grew up in an old French village, with medieval French churches, Baroque French houses and town hall, where bakers still make the traditional bread, brewers the traditional beer, and vinters the traditional wine, you might have some notion of what being French means. Certainly, not all aspects of cultural identity are created by and enforced from up top, but are drawn from local culture.
However, that doesn't mean the being French in the 24th century is the same thing as it does today, or that it did in the 17th century. There is a greater degree of homogeneity today than their used to be, and I suspect there will be less in the future.