What is the main tension between Hans Jr. and his father?

Hans Junior is a soldier and fanatical Nazi. Hans Senior is not a Nazi, and he blew his chance to join the party for painting over anti-Jewish slurs. The father and son argue fiercely; Hans Junior accuses his father of being disloyal to Germany and asks why Liesel isn't reading Hitler's book Mein Kampf. Hans Junior then calls his father a coward for doing nothing while "a whole nation cleans out the garbage and makes itself great" and storms out.