Well, the administrative regions we have are mostly the result of a previous invasion. And the cultural regions are based on the movement of people permitted by the previous invasions, and the requirements of the current invaders. France is a unified whole mostly as a fiction. Sometimes those fictions come apart at the seams - as in Scotland and Catalonia. Other times, an alternative administration can really smooth things out - as in contemporary China, France and Germany (deliberately subdivided to prevent the seams from ripping by building patches rather than merely stitching things together).
Britain-France would've had lots of scope. Past monarchs, local loyalties, language differences. If the administration wanted to, they could've succeeded.
Britain-France would've had lots of scope. Past monarchs, local loyalties, language differences. If the administration wanted to, they could've succeeded.