As Gene leaves the gym and walks across the fields for one last time as a new graduate of Devon School, the school is already being taken over by the military, the immediate future that is waiting for Gene. He hears the drill instructor barking out orders for the men doing exercises and then setting the pace as the soldiers marched to wherever they were going next. Without being aware of it, Gene responds to the orders - "my feet of course could not help but begin to fall involuntarily into step with that coarse, compelling voice."
However, the prospect of entering the military, the possibility of becoming involved in the fighting, the potential danger of being shot or killed no longer frightened Gene. He "was ready for the war, now that I no longer had any hatred to contribute to it."
Gene had done his fighting while he was at Devon. Struggling with the fear and competition and intimidation and jealousy and all the other emotions that had assaulted Gene during his time at Devon had been his war. Now, filled with the tranquility he had learned from Finny, Gene had come to understand that the greatest war of all is the war one fights within oneself. Gene had gone through that battle already and had come out on the other side, having achieved for himself "a separate peace."