Led away after Dutch leader's victory to diminish (7)
I believe the answer is:
dwindle
'diminish' is the definition.
(I know that dwindle is a more specific form of the action diminish)
'led away after dutch leader's victory' is the wordplay.
'away' indicates anagramming the letters (letters move away from their original places).
'after' says to put letters next to each other.
'leader' says to take the initial letters.
'victory' becomes 'win' (a win is a victory).
The initial letter of 'dutch' is 'd'.
'led' is an anagram of 'dle'.
'd'+'win'='dwin'
'dle' after 'dwin' is 'DWINDLE'.
'to' acts as a link.
(Other definitions for dwindle that I've seen before include "Peter out" , "Become gradually less or smaller" , "Become smaller or fewer" , "Degenerate" , "Diminish gradually" .)