Acts of warfare (11)
I believe the answer is:
hostilities
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">acts of warfare</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for hostilities that I've seen before include "Fighting" , "Acts of warfare" .)