One Spice Girl divides an arsy-versy nation (7)
I believe the answer is:
nigeria
'nation' is the definition.
(Nigeria is an example)
'one spice girl divides an arsy-versy' is the wordplay.
'one' becomes 'i' (Roman numeral).
'spice girl' becomes 'Geri' (Geri Halliwell).
'divides' means one lot of letters goes inside another.
'an arsy-versy' becomes 'na' (I can't explain this - if you can you should give a lot more credence to this answer).
'i'+'geri'='igeri'
'igeri' going into 'na' is 'NIGERIA'.
Can you help me to learn more?
(Other definitions for nigeria that I've seen before include "African country, capital Abuja" , "African country r" , "West African republic" , "Possible home for African" , "part of Africa" .)