Hemingway's Farewell To Arms deals frequently with the topic of war, masculinity, death, existentialism, and love. The novel's main theme, however, seems to be mankind's inescapable placement against two polar opposites, love and violence.
Henry experiences horror, utter brutality, and gruesome violence throughout his time served in the war. He and his fellow soldiers are often broken down and shaken to their core by the senseless violence that surrounds them. They aim to be traditionally masculine men, brave and heroic, but more often than not they buckle under the pressure.
Juxtaposed against these scenes are passages depicting Henry's limitless love for Catherine. Where war offers acts of violence, torture, and murder, their love offers acts of sexuality that, while physical, couldn't be further from the savagery of war. Furthermore, much of the couple's love comes from the violence; Catherine's fiancé is killed, and she buries her sorrow in Henry. Meanwhile, Henry, unable to cope with the depressing nature of his experiences, escapes from the horrors through his love for Catherine. They aim to escape the war together, literally and figuratively. They continuously find themselves deeply in love, scarred by the war, and unable to escape tragedy.