Why is this story an allegory?

The whole story is considered as being an allegory for the war, as implied in the title. Thus, the author wanted to convey a simple yet complex message to her young readers about a very serious subject matter and to do that she decided to come up with an allegory about the horrors of the war, presented in a clear and simple way, easy to understand and transform into a moral lesson. This title or story represents how the Nazis or terrible things did something bad and there is no one left to save the intended victims.