Barcelona, Catalonia, Spain: As you may have guessed, the Catalan area of Spain is another "restive region" that would like independence or at least more autonomy. The separatists already have a flag design; if you know what to look for you'll see it on display here and there in Barcelona.
European nations generally haven't done good jobs of integrating their varied regions into single nationalities. Americans see this and wonder why it is so difficult for the Europeans? I have a hunch.
I hypothesize the key variable is the non-immigrant status of European regional populations. A Catalonian's ancestors have probably lived here since Roman times, or before.
He has no sense that his ancestors came here to "join Spain." Rather his sense is that something called "Spain" came along and annexed his native soil and it's inhabitants - his ancestors - almost certainly without asking first.
So a Catalonian or a Basque or a Fleming or a Breton or a Norman or a Catholic in Northern Ireland, etc. may feel like a draftee instead of a volunteer, like someone whose ancestors were "press ganged" into the nation.
By contrast the largely immigrant nations of the Anglosphere (Australia, Canada, New Zealand, the U.S.) have created populations that substantially identify with their new "homelands-of-choice." Exception: Canada hasn't integrated Quebec, and probably won't either. Quebec isn't a volunteer, but a conquered former colony of France.
The small aboriginal populations of these four immigrant nations have failed to thrive, or to integrate. This can be seen as further evidence of the hypothesis at work.