After killing the enemy sniper, the protagonist, "the sniper," decided he wants to see the man he has killed. He even considered the fact that he might know his victim:
He wondered did he know him. Perhaps he had been in his own company before the split in the army. He decided to risk going over to have a look at him.
When the sniper finally reaches his victim, he discovers that the victim is his "brother." This could be taken quite literally, that in a civil war, one might be fighting against his own brother. It could also be taken figuratively in that fighting in a civil war, one is essentially fighting against his brothers (countrymen), being related by nationality, culture, etc. The wider implication is that considering all humans are siblings simply by the fact of all being part of the human race and experiencing the same human condition, any war is (in this grand scheme of things) a war of brother against brother.
That being said, this particular story shows how, in a civil war, actual biological brothers could become enemies.