The setting of the Civil War is intrinsic to the plot of Ambrose Bierce's story, "An Occurrence at Owl Creek Bridge." Without this war, there would have been no soldier for Peyton Farquhar to have learned about the bridge from; the Federal scout, as he was later revealed to be, would never have been in Alabama. There, then, would never have been any motive for Farquhar to blow up the bridge had there been no Civil War. And, there would have been no story.
The war, therefore, is absolutely essential to the plot. For, it provides Farquhar the romantic motivation to be heroic. He departs from his family only for something greater: his love of country. He, then, becomes the sacrificial victim to a cause, hanged, swinging gently and senselessly from side to side beneath the boards of the Owl Creek bridge. Within the setting of the war, Peyton Farquar is an object of satire: He has died because of his Romantic notions of war.