This set of lines is really interesting to me. I believe what it's referencing is the harsh terms of the treaty of versailles after WWI which placed Germany wholly responsible for the war. These harsh treaty terms are blamed by many for the severity of the economic depression that led to Hitler and the Nazi party ascending in Germany. Auden's words suggest that this result is obvious by stating that it is "What all schoolchildren learn." The blunt final line of the stanza and the enjambment which leads up to it further hammers the point home through the abrupt manner in which the passage ends. It almost seems like something is missing.

This section is a clear allusion to the Shakespeare play "The Tragedy of Hamlet, Prince of Denmark." If you haven't read it, it's certainly an essential piece of literature. To highlight some of its important themes, however, it features a great deal of musing on the nature of death. One of its most iconic scenes shows Hamlet holding the skull of the dead court jester Yorick.

To me, the point of this allusion is to further emphasize the narrator's risk adverse nature. He's no prince hamlet, but rather like an advisor or even a fool.

The enjambment here gives this stanza a distinct, human feel. It enhances the sense of indecision which is core to the narrator's self-questioning in this section. I also think its interesting that the questions at the start of the stanza are in quotation marks, while the repetition at the end is not. This makes the statements at the end seem more like internal questioning than something said to the implied interlocutor.

This seems to me to be an allusion to the Sphinx. In Greek tragedy Oedipus, the Sphinx gives riddles to passerbys of Thebes and killed those who could not answer the riddle (Citation. This allusion may be meant to evoke the horror of Oedipus killing his father and marrying his mother, something obviously horrendous.