Nazi-Germany's message to the black soldiers

The first time I saw this in the movie with the female German woman speaking to the black men through loud speakers, I was curious what the Nazi's were trying to convince the black troops of exactly, like were they trying to get them to defect and join them? It'd be an odd thing given that an army of Nazi's would try to recruit black-Americans to join them. Well, I went on Yahoo Answers and asked, and I was told that it was a propaganda technique to demoralize the soldiers.

I also recall when watching "Roots: The Next Generation", during a battle scene taking place during World War I, a group of black troops had received a propaganda leaflet of some sort that the Germans dropped off behind enemy lines through their jets pretty much saying the same thing that would later be said to the black men in World War II.

Why I am so intrigued by that is because I have been studying another war recently - The American Revolution, and during that war, the British promised any black male slave that escaped from their masters and served with them would win their freedom after the war, and it reminded me of what the Germans would later do over one-hundred and sixty years later.....kinda disturbing if you think about it...that's a big gap, and black people were still beig mistreated in the U.S.A., and enemy troops were still playing off that.

Does anymore information about the Nazi propaganda that they were trying to sell to the black soldiers? i.e. A site, a book, etc, that explains this in detail, or if you know about it, please share whatever knowledge you have below.