A conflict is clash or tension between opposing forces. These forces could be internal or external. When the conflict is that of “man vs. man” and “man vs. nature”, it is external. In simple words, something external to the character causes trouble. When the conflict is between “man and himself”, it is internal. In Liam O’Flaherty’s The Sniper, the conflict is both internal and external. The story is set in Dublin during the time of Irish Civil War. The republican sniper has to deal with the turbulent surroundings of the wartime. Together with this, he also has to deal with an enemy sniper sitting on another rooftop across the street. Both these troubles constitute as external conflict in the story. The internal conflict is the emotional or mental struggle that the republican sniper deals with after he kills the enemy sniper. He gets uncomfortable seeing the enemy sniper fall down and feels deep guilt and remorse. And then he sees the face of his own brother in the enemy sniper and feels the ultimate conflict within himself for having murdered him.
The other answer on The Sniper is what you need to answer your question. In addition, I would add that the internal conflict is deeper than indicated. The sniper battles himself over the idea of killing the other man, using all his skills to figure out where he is. He knows he has to kill the man without exposing his own position, but wonders how the world he lives in came to this. He was not a sniper in ordinary life, but has become an expert at killing which is not what he expected or even wanted. When the enemy sniper falls, the republican sniper does feel a sense of victory, that he has outsmarted the enemy. However, on the heels of that victory comes the regret that another person had to die at his hand. When he sees that the other sniper is his brother, again he feels regret at the death of another man in his homeland, and yet the story has him leaving the body behind as he joins up with his group, showing the dichotomy of regret, satisfaction that the other man is dead and not him, sadness that it is his brother, and then the odd war time joining with his group to continue the war and thus the killing. The conflict swings often between external and internal in this story, and illustrates the mental gymnastics required to stay sane during wartime when killing your own brother must be emotionally justified.