WordNet (r) 3.0 (2006):

encirclement
    n 1: a war measure that isolates some area of importance to the
         enemy [syn: blockade, encirclement]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "encirclement":
   aerial tactics, airborne tactics, applied tactics, armored tactics,
   barrier tactics, beleaguerment, besiegement, blockade, blockading,
   cavalry tactics, cincture, circling, circumambience,
   circumambiency, circumcincture, circumflexion, circumjacence,
   circumposition, containment, defensive strategy, diversion,
   embracement, encincture, enclosure, encompassment, enfoldment,
   envelopment, environment, feint, fire tactics, girding, girdling,
   inclusion, infantry tactics, infiltration, investment, involvement,
   mob tactics, mobile tactics, pincer movement, pincers movement,
   shock tactics, siege, strategy, surrounding, tactics,
   vertical envelopment