What literary device does Bierce use to give the reader a vital backdrop for the story?
In "An Occurrence at Owl Creek Bridge," Ambrose Bierce uses exposition to give the reader crucial background information on the main character, Peyton Farquhar, and his motivations for attempting to burn the bridge. This exposition is key to our understanding of why he would do what he did and why he's being hanged for it.
The entirety of Part II provides this vital exposition. We learn that Farquhar was a plantation owner, a slave owner, and a secessionist (one who wanted the South to permanently separate from the Union around the time of the American Civil War). Although he did not join the army, he was a "civilian who was at heart a soldier," and he was willing to perform any task in order to help the South retain its way of life. He learns from a man he does not realize is a Federal scout that
"The [Union] commandant has issued an order [...], declaring that any civilian caught interfering with the railroad, its bridges, tunnels or trains will be summarily hanged."
Such an order communicates just how important the railroads are to the Northern war effort, and so Farquhar -- with his belief that "all is fair in [...] war" -- determines to aid the South by disrupting the railroad lines on which the North relies. Without our having this knowledge, he's just a man being hanged who happens to hallucinate in the moments before his death. Bierce's exposition adds content and depth to both character and theme and is therefore crucial to our understanding of both.
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