The barbed wire fence is a physical separation between Bruno and Shmuel. What other types of separation does the fence represent in this story?

The fence becomes a metaphor for the separation between Germans and Jews. The Jews are treated very much like zoo animals. The fence also separates humanity. The Germans outside the fence carry on with their lives as if everything is normal where the Jews must survive with a death sentence on their heads. There is a largely a sense of respect and order outside the fence where as inside the fence there is only domination and suffering.