If there has been a time during which German music has been slightly more distinct from other European countries, it was the first half of the 20th century.
Popular music in the late 19th and early 20th century was almost inextricably linked with the operetta, a light form of the opera, with trivial plots, dialogues between the music and more or less also lighter music. Centers of the operetta were Berlin and Vienna. Many operettas contained one or more songs which became famous hits.
It was also the time in which the popularity of march music was at it's peak. Germans were proud of having become a world power, and demonstrating it's strength, enormous patriotism, as well as military culture became sort of a life style. This was especially the case in Northern Germany which stood in the tradition of Prussia's military culture.
Famous march of the operetta "Frau Luna" by Paul Lincke 1899. Berliner Luft - the Air of Berlin
The 1920's, the Weimar era, was characterized by the cabaret. Besides a lot of shows in Berlin (my grand-grandfather was a conductor at a cabaret, BTW), also many records were produced which were sold in high numbers to the average population. Most of these songs were swaying between political satire, sexual hints as well as complete non-sense.
She has a big Nazi, she has a small Nazi. She likes them both very much and is an expert in Nazis so to say (but spurns everything that's got style)
What are you doing with your knee, dear Hans, while we are dancing? (You are so disgusting!)
Comedian Harmonists with "A little green cactus is on my balcony"
When the Nazis came to power they set an end to that sort of culture, to prevent further political critisism and fornication. Popular songs became trivial with low intellectual demand. During WWII many songs were about hope and staying power, like rallying calls for the population.
Ironically, and for the same reason, the same songs partly also became anthems of the opposition and the persecuted. This was highlighted in the fact that the most important Nazi-composer of that time, Bruno Balz himself spent much of is time in Gestapo inprisonment (because of his homosexuality), but was still asked to compose these songs.
Bruno Balz composed this song for the movie "Die grosse Liebe" in 1941, sung by Zarah Leander, while he was in prison. Without intention of the Nazis, this song became an anthem of the persecuted.
"Davon geht die Welt nicht unter" - "It won't be the end of the world - because we still need it tomorrow"