Invader's tactic

SIEGE

Think of a prolonged military blockade often used to cut off supplies and force surrender, like surrounding a castle.

"Invader's tactic" points to "SIEGE" because it describes a military strategy where an army surrounds a place to cut off supplies and force surrender. The word is straightforward here—no wordplay or hidden meanings—just a direct reference to a common historical warfare method. Think of famous sieges like Troy or Leningrad to connect the clue to the answer.