nationalism

More precisely, where does one civilization end and another begin? I'm certain pretty much everyone here have at some point had a heated debate about this, including yours truly, but never in a thread specifically about this subject, which is why I'm creating one. I could start off by listing...

I'm playing as England on Historical Earth, on King level. I have attained the Nationalism Civic, but I can't form corps with my Redcoats or a fleet with my Sea Dogs or Caravels. Is this a bug? I didn't have this problem in my last game as Russia on random map, Prince level.