This question astutely draws attention to the way in which this great novel can be considered a war story. However, what is interesting about it is the way that war dominates its pages even though we never see soldiers facing the reality of war on the battlefield. Instead, it focuses on male adolescents who do not know the horror of conflict. The main characters of this novel show the ways in which boys who were approaching the age of being drafted were obsessed with the war.
What is interesting about the war effort is that none of the characters seek to avoid military service. This is shown in the reaction of the major characters: military service was not questioned. What was debated is the timing of being called and the branch of military in which they wanted to serve. Therefore, the focus of this novel is not so much the actual war as such but its impact on those who anticipated serving in it. Note what the author himself wrote about the impact of war on his life:
The war was and is reality for me. I still instinctively live and think in its atmosphere.
This is why the novel clearly is full of references to war and the adolescent boys think and breathe the war to such a great extent, that even their games are reminiscent of war and allude to it. Even Finny's decision to ignore the war and pretend it is not happening is shown to be something that changes as the characters lose their innocence and are forced to accept the brute realities of life. The way in which each of the characters has to come to terms with war and what awaits them indicates the sense in which this novel is a coming-of-age work that focuses on the development and maturity of these characters.