Source : Webster's Revised Unabridged Dictionary (1913)

Belligerence \Bel*lig"er*ence\, Belligerency \Bel*lig"er*en*cy\,
   n.
   The quality of being belligerent; act or state of making war;
   warfare.

Source : WordNet®

belligerency
     n 1: hostile or warlike attitude or nature [syn: {belligerence}]
     2: acts of overt warfare; "the outbreak of hostilities" [syn: {hostility}]