Takes advantage of United States and Spain (4)
I believe the answer is:
uses
'takes advantage' is the definition.
(I've seen this in other clues)
'united states and spain' is the wordplay.
'united states' becomes 'US' (abbreviation for the United States).
'and' is a charade indicator (letters next to each other).
'spain' becomes 'es' (es is an abbreviation for Spain).
'us'+'es'='USES'
'of' is the link.
(Other definitions for uses that I've seen before include "Takes (drugs)" , "Utilises" , "Employs" , "Puts into service" , "What an employer does" .)