Can counter-propaganda by a foreign democratic country help to overthrow an authoritarian military regime? And if so, what are the mechanisms through which this happens? We analyze these questions in the context of the Nazi-fascist occupation of Italy during WWII. We study the effect of BBC radio counter-propaganda (Radio Londra) on the intensity of internal resistance to the Nazi-fascist regime. Using variation in monthly sunspots activities affecting the sky-wave propagation of BBC broadcasting towards Italy, we show that BBC radio had a strong impact on political violence. We provide further evidence to prove that BBC radio played an important role in coordinating resistance activities, but had no lasting role in motivating the population against the fascist regime.