I prefer to call it "modern-western-culture". After all, the USA is a nation, France is a nation, England is a nation, The Netherlands is a nation, etc, but all these nations are part of one civilization: the modern-western civilization.
In the game, this civilization is represented by the USA. Of course, the English and the French are also in the game, but they represent their respective civilizations before they together formed what is now "western civilization."
Thats how I always interpreted it.