In The Boy in the Striped Pajamas, Bruno's father's reply to his question shows his embrace of Nazism.
Bruno approaches his father in Chapter 5 because he is unhappy about having to live at "Out-With." Bruno misses his home and his friends. He speaks with his father because he wants to go back to Berlin. Predictably, Bruno's father rejects the idea of returning. Before Bruno ends the conversation, he asks his father about the "people outside" and receives a very telling reply: "They’re not people at all...at least not as we understand the term....You have nothing whatsoever in common with them."
Bruno is "uncertain" of what his father's response means and leaves the conversation "unsatisfied." The response reflects how much Bruno's father supports Nazism. He sees his position at Auschwitz as a move that benefits his career. This compels him to emphasize to Bruno that the people outside are "not people at all." Boyne uses his response to show how many Germans under Nazism responded to the Holocaust. They did not see what they were doing as genocide and cruelty because they could not see their victims as human beings. They were not "really people." Bruno's father's response displays this rationalization, something that Bruno himself could not understand.