Examples of songs that changed something is a fine old thread with some examples.

A song that altered history? 'Granola Vila Morena' perhaps, though it could be argued that any other song could just as well have triggered that revolution.

In the history (before '45) of the German armies there have always been forbidden songs. You could get punished for singing them. If the people deciding about censoring such songs thought these songs might have a possible detrimental effect on the military, we should seriously consider the possibility they were right.

Wolfgang