In the interwar period, the House of Habsburg was a vehement opponent of National Socialism and Communism. In Germany, Adolf Hitler diametrically opposed the centuries-old Habsburg principles of largely allowing local communities under their rule to maintain traditional ethnic, religious and language practices, and he bristled with hatred against the Habsburg family. During the Second World War there was a strong Habsburg resistance movement in Central Europe, which was radically persecuted by the Nazis and the Gestapo. The unofficial leader of these groups was Otto von Habsburg, who campaigned against the Nazis and for a free Central Europe in France and the United States. Most of the resistance fighters, such as Heinrich Maier, who successfully passed on production sites and plans for V-2 rockets, Tiger tanks and aircraft to the Allies, were executed. The Habsburg family played a leading role in the fall of the Iron Curtain and the collapse of the Communist Eastern Bloc.