Was the situation presented in "The Sniper" real? Could it happen today? What conditions are necessary for this type of thing to happen ?

Liam O'Flaherty's short story "The Sniper" is based on true events. Judging by information in the first paragraph of the story, it must be assumed that the setting of the story is the Battle of Dublin in June and July of 1922. That battle was centered around the Four Courts building in the center of Dublin. During the battle, Republican forces held some of the downtown streets and definitely used snipers perched on rooftops to control the activities below. It is also known that the author of the story was in Ireland during the war. Whether or not the exact situation in the story was true cannot be known, but it is for sure that members of the same family did fight on opposite sides during the war.

Scenarios similar to this are probably happening right now somewhere in the Middle East, Asia or Africa. In countries like Syria, Afghanistan, Yemen, Libya and elsewhere families are being torn apart by conflict. It has been widely reported that the rebel groups in Syria, who had been united in fighting government troops, are now fighting each other. Civil wars are usually fought over some basic principle like a political or religious goal. The Irish Civil War was fought over just such a disagreement. One side favored the Anglo-Irish Treaty and the other side did not. The same conditions could occur in a country where there are deep conflicts over important ideas as is currently happening in several places across the globe.