The current unstoppable advances by "Islamic State" and its armies of terror in Iraq make me remember a short-short story that I read, I think, in the post-Vietnam era (late '70s).
Can't remember much except one word that is featured prominently: Teeth.
The narrator tells of reports coming in, first from outlying provinces, then drawing nearer and nearer. Like a river of Amazonian ants, the invaders devour everything in their path. A number of efforts to mount a brave resistance all fail.
I'm not sure now if the moniker "Teeth" is just metaphorical or if the story is set in some post-apocalyptic/alternative universe where some humans have mutated into giant jaws on two feet, with little else in the way of body parts.
The general feel of the story was one of anomie, hopelessness and desperation. It might have been a Robert Silverberg story or one of someone inspired by him.