How does World War II intrude on the lives of the boys, and how does it influence the boys' behavior and relationships?

In John Knowles's classic A Separate Peace, World War IIis an ever-present specter at the school. This is seen in how the students are treated by staff and how the boys play games.
One of the first hints as to the impact that the war has on the boys' lives is through how they are treated by the teachers. The older boys are held to strict codes of behavior that will serve them in the army. The younger boys experience some leniency, as the teachers look at them with an understanding that these boys will have a very short childhood and should take full measure of the time they have to be kids.
The influence of World War II can also be seen in the games the boys play. Blitzball, the game that Phineas invents, is an example of the language of the war seeping into Devon School. Blitz is taken from the German war tactic Blitzkrieg. Phineas is obsessed with the war, and it is this obsession that leads to the creation of this game. It is not only through Blitzball that the war’s influence can be seen. Phineas has a desire to prove his fitness for military service and takes the activity of jumping out of a tree into the water as not just a game but as training for the military. He says to Gene that there would not be time to think if they were on a ship that had just been torpedoed: they would have to jump.
All the boys are influenced by the war, but none more that Phineas. For Phineas, the war means everything—from worrying that it will be over before he can serve to contacting every branch of the military when an injury prevents him from service in the army.