What indicates the way for war or revolution (5)
I believe the answer is:
arrow
'what indicates the way' is the definition.
(an arrow gives directions)
'war or revolution' is the wordplay.
'revolution' indicates anagramming the letters.
'war'+'or'='waror'
'waror' is an anagram of 'ARROW'.
'for' is the link.
(Other definitions for arrow that I've seen before include "Item in a quiver" , "Missile of the archer" , "Pointed projectile" , "Weapon from bow" , "Quarrel, fired from crossbow" .)