Postcard advertising the 11th NSDAP Party's Nuremberg Rally of 1939 ("Rally of Peace") that never happened. It was canceled last minutre, as the invasion of Poland started just a day before planned event. 
The theme of the rally, ironically, was the peace. United Great German Reich, booming economy and abundance are symbolized by the image on the front of the card. There's a pre-printed postage stamp with Adolf Hitler on the back. 
 
Faithful reproduction of the postcard from Krause Papierwerke.