Revolutionary peasant can have military leaders' opponents as guards (8)
I believe the answer is:
watchmen
'guards' is the definition.
(I know this)
'revolutionary peasant can have military leaders' opponents' is the wordplay.
'revolutionary peasant' becomes 'Wat' (Wat Tyler led the Peasants' Revolt).
'leaders'' indicates taking the first letters (I've seen 'leaders' mean this).
'opponents' becomes 'EN' (East and North players in the card game bridge).
The initial letters of 'can have military' is 'chm'.
'wat'+'chm'+'en'='WATCHMEN'
'as' is the link.
(Another definition for watchmen that I've seen is " Sentinels".)