The Collaborative International Dictionary of English v.0.48:

Demobilize \De*mob"i*lize\, v. t. [Cf. F. d['e]mobiliser.]
   (Mil.)
   To disorganize, or disband and send home, as troops which
   have been mobilized.
   [1913 Webster]

WordNet (r) 3.0 (2006):

demobilize
    v 1: release from military service or remove from the active
         list of military service [syn: demobilize, inactivate,
         demobilise] [ant: call up, mobilise, mobilize,
         rally]
    2: retire from military service [syn: demobilize,
       demobilise, demob] [ant: mobilise, mobilize]