@layman,
When Attila the Hun, and his teeming yellow horde, came across a western city surrounded by walls, he would call one of his trusted generals to ride up next to him.
Then, in full sight of the inhabitants manning the towers, he would take out his sword and chop off that general's head.
Then he would yell: "If that's what I do to my own homeboys, what in the **** do you think I'm gunna do to you if you put me to the trouble of busting down your walls, just to get your gold, and ****?"
Invariably, after a little reflection, the gates would swing open.
Then the hordes would trot on in and take everything of value, including the (attractive) women. After killing every sorry inhabitant of the city first, of course.
Now, that's what I would call "effective," ya know?