"Do media broadcasts matter when they reach audiences that are not their target? In a conflict, the media may have an unintended effect of increasing ethnic animosity. We consider radio signals travelling across country borders in the region that witnessed one of Europe's deadliest conflicts since WWII: the Serbo-Croatian conflict in the Yugoslavian wars. Using survey data, we find that a large fraction of Croats listen to Serbian radio (intended for Serbian listeners across the border) whenever signal is available. Then, using official election results, we document that residents of Croatian villages with good-quality signal of Serbian public radio were more likely to vote for extreme nationalist parties, even after several years of peace time. Finally, ethnically-offensive graffiti are more likely to be exposed openly in the center of villages with Serbian radio reception. The effect is identified from the variation in the availability of the signal mostly due to topography and forestation. The results of a laboratory experiment confirm that Serbian radio exposure causes an increase in anti-Serbian sentiment among Croats"--National Bureau of Economic Research web site.