How does Ambrose Bierce present the theme of war in "An Occurrence at Owl Creek Bridge"?

Ambrose Bierce starts his story as if it is only a single trivial incident taking place at an unimportant wooden bridge that does not even span a river but a creek that nobody has ever heard of. He chooses not even to give the name of the man who is about to be hanged, and he has nothing to say about what the man did to get himself into this situation. This is just an incident in a war that eventually claimed the lives of some 620,000 soldiers. Why should this man's experience or his final fate be of any special importance?
Then, in Part 2 of the story the author identifies the doomed man and shows the reader his lovely wife and his beautiful, peaceful plantation. We are beginning to realize that this man was not just a number but a real human being with all the same feelings as ourselves. And in Part 3, when we are led to believe that Peyton Farquhar might have a chance to escape back to his home and his wife and children, we not only know his name and his status, but we are made to identify with his hopes and fears and all his other feelings. The story tells us that each of the men who died in the Civil War was a real human being just like ourselves. All of them wanted to live. None of them wanted to die—and most of them did not expect to die. Most of them were motivated by patriotism, a sense of duty, and a desire for glory.
The plan of Ambrose Bierce's story is to move from the general to the particular, from the formal ceremony of a military hanging into the mind and heart of a single hapless, misguided individual. By the time the body hangs below the Owl Creek Bridge, swinging slowly back and forth, we know this man and have lived through his experiences with him right up to the point where he almost clasps his wife in his arms. We realize the horror and insanity of war.