"Salvador" by Lucius Shepard

In this short story, Shepard serves up an incredibly distrubing tale of the effects of war with a Science Fiction / Fantasy twist. It follows Dantzler, a Special Forces soldier during a fictional (although not implausible, especially for when this story was written in the 1980s) war of American conquest of South America. There are a few small Science Fiction elements mixed in, largely in the form of government-supplied Ampoules of what appears to be souped-up PCP (again, not entirely implausible), along with, as the story progresses, a heavy mix of Fantasy through the application of the myths and beliefs of the Santa Ana tribesman of El Salvador.

However, if you set the Fantasy and Science Fiction elements aside, you can see that Shepard's true thrust in this story is the inhumanizing effect of the horrors of war. In the character of Dantzler, Shepard shows the effects of war and how a normal person can become so hollowed-out by it, so devoid of emotion, that they become capable of unspeakable acts. Every aspect of this story is tragic, yet, especially if you think of the Fantasy elements as the disintegration of Dantzler's sanity, distrubingly plausible. And that is probably the most unsettling aspect of this story: You can clearly see how Dantzler's experiences make him into the "person" that he is at the end of the story.