How does the theme, mans inhumanity to man, relate to a separate peace?

Throughout the book there is always WW2 looming in the background. The violence and fear of war always casts a shadow over Devon. There are plenty of social conflicts in this book. I wouldn't say they were a severe as many issues in our collective history like slavery or genocide. They are however part of the social framework of these boys. Gene and Finny have this dysfunctional co-dependant rivalry going. Gene shaking the tree and causing Finny's fall was an example of cruelty but I don't think the injury was intentional. THe character of Brinker seems to derive pleasure from social conflict. Brinker Hadley is

one of Gene's friends, and his main rival for the top academic spot in the class. Brinker makes long-running jokes with rather sinister undertones. He is determined to cause turmoil simply to watch things unfold.