In fact, I've just realised that if you want to run around splitting the world up into cultural groups then Europe and the Mediterranean basin and stretching through the Arab world is a natural grouping: shared religion, significant ancient trading and political links,  shared philosophical and political heritage to a large extent until very recently.

Including the Arab world here is a hill too far for me.  political heritage is very hard to see--autocracy vs. democracies primarily.  philosophy greco/roman through all of the western schools, how does that link to arab philosophies.  politics--treatment of women certainly doesn't tie in.  certainly not today, but not 400 years ago either.  yes the religion is grounded in some ways with christianity and Judaism, but the tracks the religions have taken are totally different.  acceptance of new trends, secularism--pretty big difference.  importance of education, economics--totally different.  Arab world still stuck on interest charges being a sin.  I just can't see it.