Liam O'Flaherty's short story "The Sniper" is one in which a Republican sniper must "take out" an enemy sniper. This sniper is perched on a rooftop across form him. In the end, the Republican sniper proves himself to be worthy of his position--he is able to kill the opposing sniper. When the Republican sniper checks on the identity of his victim, he finds that it is his brother.
Essentially, the story tells about a soldier who is defined by his position. He is a sniper and will do whatever it takes for success. The brutal truth is that people around him are dying. Not only do many people die in front of him, he kills his own flesh and blood.
The horror of war is that, when one looks at the bottom of it, people are killed. The sniper does not think about the person he is aiming at. According to the story, the only reason he wishes to know who the man is results from his thoughts that he may know the man. Unfortunately, the sniper did know the man.
This idea, and image, has been seen many times throughout history. The Civil War in America placed father against father and brother against brother. The horror of war, in the end, is that mankind is eliminating the chance for humanity to continue, for bloodlines to continue. Not knowing who the enemy is, getting the enemy in one's sights, and pulling the trigger is normally done not knowing the person on the other side of the gun. It is not until one recognizes the fact that they could begin to question what they are doing.