The book’s title indicates its central theme—The War with Grandpa translates to conflict within families, but there are other family conflicts as well. Conflicts often occur within families, and Peter’s family has many of them. He has conflicts with Jennifer, and he has preexisting conflicts with his parents, who make him take piano lessons, yet the conflict over the room is especially significant to Peter because it encroaches on his beloved territory.

To a child, a bedroom may be the only space of their own, so its loss can feel overwhelming. When Peter is forced to move out of his bedroom so his grandpa can have it, he is devastated. He tries to talk with his parents, but they cannot conceive of another solution that will be as comfortable for Sally’s father. The absurdity of comparing lethal war to a conflict with a family member is funny, but it underscores the depth of childhood emotion. Peter’s parents underestimate his attachment to his room and do not engage him in the decision-making or problem-solving process. As a result, Peter goes to war with his grandpa even though his real issue should be with his parents. He copes with the loss of his bedroom by blaming his grandfather because his parents have been unyielding in their decision.