The Collaborative International Dictionary of English v.0.48:

externalization \externalization\ n.
   1. attributing to outside causes.
      [WordNet 1.5]

   2. embodying in an outward form.

   Syn: externalisation, exteriorization, exteriorisation.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

externalization
    n 1: attributing to outside causes [syn: externalization,
         externalisation]
    2: embodying in an outward form [syn: externalization,
       externalisation, exteriorization, exteriorisation]