Decreased staff controlling Spain (5)
I believe the answer is:
waned
'decreased' is the definition.
(waning is a kind of decreasing)
'staff controlling spain' is the wordplay.
'staff' becomes 'wand' (wand is a kind of staff).
'controlling' indicates putting letters inside.
'spain' becomes 'e' (abbreviation for Espana).
'wand' enclosing 'e' is 'WANED'.
(Other definitions for waned that I've seen before include "grew faint" , "(Of moon) grew smaller" , "Ebbed; declined" , "Decreased in size" .)