Frank Capra did a masterful job taking the propaganda tool of the Nazis and turning it against them. He devised the simple but effective means of taking captured Nazi propaganda newsreels and showing them with new narration and with music. The result -- showing the Nazi horror for what it was.
The WHY WE FIGHT series of 7 films is still very powerful and moving. We can only imagine how rousing the material was in the dark days of World War II when it was shown to the US troops in battle zones.
The difference between Capra's propaganda and Hitler's is that Capra used the tool to teach ideals rather than to seduce and entrance the minds of people. Capra's films were just as strong ammunition as and tanks and planes, and they are remarkably durable after all these years. They still stand for the ideals of democracy. Such is the art of a master moviemaker.