Military blockades
I believe the answer is:
sieges
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">military blockades</span>' is the definition.<br/ ><span class="explanation-format__explanation">('siege' can be a synonym of 'military blockade')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sieges that I've seen before include "Persistent attacks on fortied places" , "army investments" , "Persistent attacks on fortified places" , "Military actions of isolation and attack" , "military blockades" .)