Military blockades
I believe the answer is:
sieges
'military blockades' is the definition.
('siege' can be a synonym of 'military blockade')
This is all the clue.
(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" .)