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In the final chapter of Knowles's A Separate Peace, Gene Forrester concludes after his return to Devon School,
...it seemed clear that wars were not made by generation and their special stupidities,...wars were made instead by something ignorant in the human heart.
I never killed anybody and I never developed an intense level of hatred for the enemy (in the war). Because my war ended before I ever put on a uniform: I was on active duty all my time at school; I killed my enemy there.
Only Phineas never was afraid, only Phineas never hated anyone. Other people experienced this fearful shock somewhere, this sighting of the enemy, and so began an obsessive labor of defense, began to parry the menace they saw facing them by developing a particular frame of mind....
All of them, all except Phineas, constructed at infinite cost to themselves these Maginot Lines against this enemy they thought they saw across the frontier, this enemy who never attacked that way--if he ever attacked at all; if he was indeed the enemy.
Gene's private evil is the same evil that causes wars; in fact, his war is the essential war: man against man. In his terrible envy of Finny, who "got away with everything because of the extraordinary kind of person he was," Gene fails to perceive the beautiful innocence and goodness that is in Finny, the peace that is Phineas. The "something ignorant" in his own heart, which is in most men's hearts, causes Gene to interpret Finny's motivations for having him go out to jump on the limb, from preventing Gene from studying or doing what he plans. In his resentment of Finny's innocent ideas, Gene jounces the limb and fatally injuries Finny, thus attacking and eventually killing his rival, his enemy. Conclusively, Gene and Phineas represent the Maginot Line, the imaginary line of defense that people and nations create in their never-ending rivalries, rivalries that often cost people their lives.