In A Farewell to Arms, Hemingway uses the plot and characters to indirectly discuss the horrors of war with his readers.  Near the beginning of the novel, the men gather with the priest and exclaim how hopeless they feel the war is.  They do not understand their role in the war or even what the war is all about.  Further, the men have been ill-equipped for fighting and, as a result, encounter significant casualties.  When Lt. Henry and his men are bombed, Lt. Henry watches some of his men die and he himself sustains a knee injury (similar to what actually happened to Hemingway during his time in Italy during the war), thus chronicling the atrocities of war.