Going Viral: Nazi Marches and the Spread of Extremism
Can extremism become contagious? Many papers have shown that social control of public actions can lead to sudden transitions from ‘extreme to mainstream’. What is not clear is whether social spillovers can also have first-order effects on private actions, like voting, where persuasion is key. We first build a measure of social interaction frequency using granular data from the 1918 Spanish Flu epidemic in Hamburg and information on household characteristics. We then examine the effects of Nazi propaganda: Neighborhoods exposed to Nazi marches saw a sharp increase in support for the Nazi party a few days later. By the following election, Nazi support had spread to other parts of the city, following 1918 contagion paths and the lines indicated by social homophily. Our results show that extremist propaganda can be effective through a “persuasion multiplier” arising from social interactions.
Hans-Joachim Voth is UBS Foundation Professor of Economics, University of Zurich.
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