What is the theme in Ship of Fools by Katherine Anne Porter?

Anti-Semitism and nationalism are themes. The voyage takes place in 1931, only two years before Hitler and the Nazis came to power in Germany, and in the novel, the Germans display a deep-seated anti-Semitism. The worst offender is Herr Rieber, the proto-Nazi. He uses the journal he publishes to disseminate anti-Semitic propaganda and proudly tells Lizzi that one the topics discussed is the idea that "if we can find some means to drive all the Jews out of Germany, our national greatness will then assert itself and tomorrow we shall have a free world." Rieber warms to the subject of the Jews over dinner at the Captain's table, talking (in the way Nazis did) about cleansing the blood of Germany from the Jewish poison. No one dissents from this except Dr. Schumann, who represents a moral sensibility well above that of the others.