The Collaborative International Dictionary of English v.0.48:

Warpath \War"path`\, n.
   The route taken by a party of Indians going on a warlike
   expedition. --Schoolcraft.
   [1913 Webster]

   On the warpath, on a hostile expedition; hence,
      colloquially, about to attack a person or measure.
      [1913 Webster]

WordNet (r) 3.0 (2006):

warpath
    n 1: hostile or belligerent mood; "the chief is on the warpath
         today"
    2: a course leading to warfare or battle

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "warpath":
   aggression, aggressiveness, antagonism, bellicism, bellicosity,
   belligerence, belligerency, chauvinism, combativeness,
   contentiousness, ferocity, fierceness, fight, hostility, jingoism,
   martialism, militancy, militarism, pugnaciousness, pugnacity,
   quarrelsomeness, saber rattling, truculence, unfriendliness,
   unpeacefulness, warmongering