Social capital is often associated with desirable political and economic outcomes. This paper contributes to the literature exploring the “dark side” of social capital, examining the downfall of democracy in interwar Germany. We collect new data on the density of associations in 229 German towns and cities. Denser networks of clubs and societies went hand-in-hand with a more rapid rise of the Nazi Party. Towns with one standard deviation higher association density saw at least 15% faster Nazi Party entry. All types of societies – from veteran associations to animal breeders, chess clubs and choirs – positively predict NS Party entry. Party membership, in turn, is correlated with electoral success. These results suggest that social capital aided the rise of the Nazi movement that ultimately destroyed Germany’s first democracy. Crucially, we examine the question when a vibrant civic society can have corrosive effects. We show that the effects of social capital depended on the political context – in federal states with more stable governments, higher association density was not associated with faster Nazi Party entry.