on the warpath

from 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]