Who is the antagonist in "Soldier's Home"?

The protagonist is the main character of a literary work whose conflict sets the plot in motion. The antagonist is the character or force which struggles against or blocks the protagonist. In Hemingway's short story "Soldier's Home" the main character and protagonist is Harold Krebs. Krebs has recently returned from service as a Marine fighting in World War I. Judging by what the third person narrator tells the reader it could be said that Krebs suffers from what was then called "shell shock" and is now diagnosed as Post Traumatic Stress Disorder. The narrator admits that during the war, Krebs "had been badly, sickeningly frightened." Back home, Krebs is depressed and somewhat anti-social. His idea is to avoid complications, consequences and for "life to go smoothly." For a time he is able to do this. Eventually, however, the antagonist, in the form of his parents, especially his father who never actually appears in the story, look to force Krebs out of his apathy by insisting he go out into the world and get a job and maybe a girlfriend. His mother tells him,

"You know we love you and I want to tell you for your own good how matters stand. Your father does not want to hamper your freedom. He thinks you should be allowed to drive the car. If you want to take some of the nice girls out riding with you, we are only too pleased. We want you to enjoy yourself. But you are going to have to settle down to work, Harold. Your father doesn't care what you start in at. All work is honorable as he says. But you've got to make a start at something."

Krebs initially rebels at his mother's suggestions but she soon shames him, crying when he claims he doesn't love her. At the end of the story he concedes that he must go to Kansas City to find a job and get on with his life. Although he would rather continue a life without consequences he must heed his parents' wishes.