Throughout John Knowles's novel, A Separate Peace, there are parallels drawn between the internal wars within the main characters and the conflicts that develop among countries. In early chapters, Finny concerns about the European conflict by stating that the war is really a conspiracy among the world's leaders. So, in the same way that Germany and the Allies convinced its youth that they were fighting for a greater cause, Finny creates
reverses and deceptions and acts of sheer mass hypnotism which were so extraordinary that they surprised even him.
As with the climate of the World War, also, as Gene narrates,
Everyone has a moment in history...when his emotions achieve their most powerful sway over him.
Thus, at Devon School, Gene and Finny and others wage their private wars. Seduced by a propaganda film, Leper enlists; driven by Leper's nonsensical comments, Brinker Hadley, the head student, is driven to enlist in order to make sense of the war for himself, and Finny creates the Winter Carnival, an attempt in the winter of despair after the war has started and his leg is broken, to create sense out of chaos. Having been coached into participating as the star of this event, Gene surpasses himself as he fights "that first skirmish of a long campaign for Finny." He remarks afterwards that he feels in this afternoon a "momentary, illusory, special and separate peace."
In a final parallel between the war and the private war in men's hearts, Gene realizes that the reason that he jounced the limb on which Finny stood and the reason that wars are waged is, as Finny remarked about the war "a conspiracy," a conspiracy in the hearts of men. For, Gene decides as Leper has called him, that he himself is "a savage underneath." Extending this truth, Gene realizes that most men are savages underneath since wars, private or otherwise, are made "by something ignorant in the human heart." As a symbol of the pureness of a some human hearts--for Finny has no envy or jealousies in him at any time--dies, just as the innocent men die in World War II, victims, like Finny, of the "something ignorant in the human heart."
From a literary perspective, Finny's death is the natural and realistic culmination of the plot. Throughout the novel, Finny has been under assault, physically and emotionally. He struggles to heal from his broken leg, to deny Gene's betrayal, and to deny the reality of the war since he will be left behind because of his injury. In the novel's conclusion, after enduring Brinker's mock trial and falling down the stairs, Finny is forced to face the truth about what had happened in the tree--what Gene had done to him--and all his defenses crumble. He is broken in body and spirit, never to be the same. All that is left for Finny is to die. For him to have recovered and gone on would not have been consistent with his character and his experiences.
Also, Finny's death serves the novel's two primary themes and draws them to their conclusions. One major theme in the novel is the loss of innocence among the young in the face of adult reality, specifically the awful reality of World War II. Since Finny is a symbol of youth and innocence in the novel, his death symbolizes the death of youth and innocence.
Finny's death also brings Gene's journey to its conclusion. The novel is essentially Gene's story, his own loss of innocence in dealing with the war and, more importantly, the truth of his own nature. It is through his role in Finny's destruction that Gene comes to understand himself, especially in terms of his fear and insecurities. Finny's death emphasizes the terrible price Gene pays for such knowledge.
Finally, Finny's death serves the novel's structure. It is so traumatic for Gene that he is compelled to return to Devon fifteen years after it occurs. The novel opens with the adult Gene visiting Devon specifically to see the two places that played such a significant role in the tragedy that had unfolded there, the tree and the marble stairs. As the novel's narrator, Gene then relives the past as the novel moves into a flashback. Had Finny not died, Gene's life would not have been impacted in such a profound way, so profound that Gene is still dealing with it fifteen years later.