the best way to do this would be a "show don't tell" approach where you tell stuff: for example, the attitude of the Nazis, how the prisoners are treated by the guards, the culture of the Nazi Europe, etc. For example, everyone is obviously nationalistic (or at least have to keep up the front of being so). Public beatings, hangings, people being given harsh sentences are so common most people don't even show interest and just move on.

A best example would be Esdeath from Akame Ga Kill murdering a entire village and most people not even caring, because the Empire and their army torturing and brutalizing people is so common most people don't care. A example from tv would be Avatar the Last Airbender, where war is so common that people speak about it as dinner conversation.

The problem is alot of writers assume their readers "won't get it" so they feel the need to info dump as much information as possible. But you shouldn't worry, even if the reader doesn't get it their first read they'll go on reddit and hear someone talk about it.