Braun, Robert, and Ruud Koopmans. "The diffusion of ethnic violence in Germany: The role of social similarity." European Sociological Review 26.1 (2009): 111-123.

In this article we develop and test an encompassing theoretical framework for explaining the geographical and temporal spread of extreme right violence. This framework combines structural factors related to ethnic competition, social disintegration, and political opportunity structures, which make certain localities more prone to exhibit ethnic violence, with diffusion variables that determine the degree to which ethnic violence diffuses across time and across localities. We employ an event history analysis of instances of racist violence in 444 German counties for the time period 1990–1995. In line with previous research we demonstrate that political opportunities, ethnic competition and social disorganization, media coverage, and the severity of previous violence are significant explanatory factors in the evolution of xenophobic violence. We further find that geographical distance does not affect the diffusion of ethnic violence when controlling for social similarity, which strongly raises the probability of diffusion across localities. This indicates that the effect of geographical distance that is found in many diffusion studies may actually be caused not by geographical proximity as such, but by the fact that proximate areas tend to be socially similar.