Military blockade (5)
I believe the answer is:
siege
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">military blockade</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for siege that I've seen before include "Prolonged attack on a fortified place" , "Military operation cutting off access" , "Surrounding and blockading of town by military" , "Offence in which fortified place is surrounded" , "Persistent attempt to gain" .)