This chapter serves as the climax of the novel, a point of no return after which all the action is, in a sense, downhill. First we saw Italian soldiers shot by their superior (Lieutenant Henry) because they were deserting. Here, Aymo is shot by his compatriots by accident, out of fear and incompetence. At chapter's end, Italian soldiers are shooting other Italian soldiers at random, simply because the latter are officers. Chaos is on the loose.
Therefore, and because Hemingway has been preparing us for this moment from the scene early in the novel when the English nurse was puzzled by his very membership in the Italian army, we do not question Lieutenant Henry's decision to desert. As he tells Bonello, "We are in more danger from Italians than from Germans." Indeed, at the end of Chapter XXX, it is all but certain that if he does not flee, Henry will be executed by the Italian military police. He really has no choice.
Also, Henry's loyalty has never been to the Italian army at large anyway, but rather to those individuals with whom he has lived and worked. The ambulance group having disbanded, he feels he has no obligation to continue on behalf of the cause — which is, after all, an abstraction.
Note the theme of declaring a separate peace. As verbalized by the Italian soldiers, who think they can end the war by throwing away their rifles, it sounds naïve and foolish. It will prove to be so by the end of the novel. Notice also the reliance of the military police on words like "sacred soil" and "fruits of victory" — precisely the abstractions that Henry told us, a few chapters back, that he mistrusts. "Have you ever been in a retreat?" asks the lieutenant colonel who is about to be shot. A retreat is concrete and specific — it is something real. The lofty terms used by the M.P.s are proof that they haven't had the sort of experience that Henry has gained over the course of the novel.
