Argentinian president, about to depart, united country (4)
I believe the answer is:
'country' is the definition.
(Peru is an example)
'argentinian president about to depart united' is the wordplay.
I cannot really understand how this works, but
'president' could be 'p' (common abbreviation eg in VP) and 'p' is found in the answer.
'united' could be 'u' and 'u' is found in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for peru that I've seen before include "Nazca, Cuzco here", "Andes republic", "Lima's country", "Mario Vargas Llosa's native land", "South American country".)