WordNet (r) 3.0 (2006):

state of war
    n 1: a legal state created by a declaration of war and ended by
         official declaration during which the international rules
         of war apply; "war was declared in November but actual
         fighting did not begin until the following spring" [syn:
         war, state of war] [ant: peace]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "state of war":
   all-out war, appeal to arms, armed combat, armed conflict, attack,
   battle, belligerence, belligerency, bloodshed, combat, fighting,
   hostilities, hot war, la guerre, might of arms,
   military operations, open hostilities, open war, resort to arms,
   shooting war, the sword, total war, war, warfare, warmaking,
   warring, wartime