What does The Boy in the Striped Pajamas (the film) say about belonging?

This is fairly interesting to assess.  I am not sure if
there is a singular answer to it.  On one level, there is an intense desire to belong on
the part of the Nazis.  As the rhetoric and propaganda increase, the Nazis are shown to
be individuals who crave belonging to and with one another.  Gretel's budding sexuality
is merged towards the ideal Nazi soldier, the personification of the ultimate human
being in accordance to Nazi ideology.  At the same time, Bruno's father is driven to
"belong" to the group of individuals that have power and to be part of that inner circle
of Nazis who are to represent "the best" in everything.  While this belonging is of the
temporal, there is another sense of belonging in the friendship of Bruno and Shmuel. 
They share a belonging to one another which lasts through and defeats contingency and
that of the temporal time period.  We see this when Bruno betrays Shmuel.  The shame he
feels and acknowledgement of their friendship afterwards is a moment of belonging where
the permanent has transcended that of the temporary.  This becomes heightened when Bruno
helps Shmuel find his father.  It is here where the theme of belonging to one another is
something that causes action to be taken in the name of solidarity with consequences
that are both horrific, but also call upon the better angels of human
nature.