The author describes the sniper as having the "face of a student, thin and ascetic, but his eyes had the cold gleam of the fanatic. They were deep and thoughtful, the eyes of a man used to looking at death." This is a young student forced to become a man and a soldier. Given that this is a man forced from innocence to engage in violence, the focus is on the tragedy of war and particularly on the minds of the soldiers themselves: stolen from innocence and thrust into violence. Thus, it is an unfavorable view of war.
The sniper then feels forced to shoot the old woman because she is giving away his location and endangering his life. The sniper then decides he must kill his enemy. In all scenarios, this is a "kill or be killed" environment. The author doesn't get into the politics of the war. Rather, he focuses on the violence of war itself. In the end, the author illustrates how tragic and senseless war is (and in particular, civil war) when the sniper finds his enemy's body and sees "his brother's face." We can take this quite literally. Or, we can take this somewhat figuratively. He has killed a fellow countryman, a brother by nationhood. Civil wars are often described as "brother against brother." As senseless and tragic as it is to kill in general, killing a "brother" heightens the tragedy.