Okay kiddo, so you know how some people can be really mean and do really bad things? Well a long time ago, there were some people called Nazis who were really mean and did some really bad things too. They wanted to control everything in Germany, including the music that people listened to.
They didn't like certain types of music, like jazz and swing, because they thought it didn't represent their idea of what "good" music should be. So they banned that kind of music and instead only allowed music that they thought was good. They even created their own type of music called "Nazi music" that they wanted people to listen to.
They also wanted to control the messages in the music, so they made sure that all the songs that were allowed to be played on the radio or in public had to have messages that supported the Nazi party and their beliefs. They didn't want people to listen to music that might make them think for themselves or question what the Nazis were doing.
This was really sad because music is supposed to be something that brings people together and makes them happy. But the Nazis didn't want people to be happy unless they were happy in the way that the Nazis wanted them to be. This is why many musicians had to go into hiding or leave Germany altogether because they didn't want to be controlled by the Nazis.
Luckily, after World War II, the Nazis were defeated and people were able to listen to any kind of music they wanted again. But it was a dark time in history when music and the arts were controlled by people who wanted to spread hate and control the minds of others.