How does the story "The Sniper" by Liam O' Flaherty highlight the futility and pointlessness of war?

I would want to argue that your question, as excellent as
it is, needs to add one word to clearly focus on the issue presented to us in this
wonderful story. Let us not forget that the war in which this story is set was a civil
war, which was infamous for dividing Ireland and still lingers on today in the form of
deep-seated divisions and long-standing rancour. In addition, this civil war, like so
many, was characterised by its ability to divide streets and even families. This story
explores this concept through the shocking realisation of the sniper at the end of the
story as he turns over his defeated enemy and realises he has only killed his
brother.

Of course, this realisation is symbolised by the
feelings of the sniper after his victory over his unknown enemy. Note how the text
describes what the sniper endures:

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The nsiper looked at his enemy falling and he
shuddered. The lust of battle died in him. He became bitten by remorse. The sweat stood
out in beads on his forehead. Weakened by his wound and the long summer day of fasting
and watching on the roof, he revolted from the sight of the shattered mass of his dead
enemy. His teeth chattered, he began to gibber to himself, cursing the war, cursing
himself, cursing
everybody.

Civil war is shown
through the devasating ending to be something that ultimately only hurts yourself.
Engaging in acts of violence against an unknown enemy is shown to be really engaging in
acts of violence against yourself. Even though the sniper is shown to be "victorious,"
really, his victory is hollow and meaningless as he realises the cost of it and the high
price that civil war always exacts from those who participate in
it.