Ethnic competition theory provides a powerful explanation for ethnic conflict, by demonstrating how variation in ethnic mobilization relates to intergroup struggles over scarce resources. However, the tendency to capture such relationships at the aggregate level, through macro-level proxies of intergroup competition, offers little insight into the processes through which ethnic grievances mobilize into contentious action. This article integrates insights from the social movements literature to address how competitive contexts crystallize into broader conflicts. Drawing on data from the civil rights-era Ku (...) Klux Klan—perhaps the quintessential case of contentious ethnic organization in the United States—the analysis focuses on the ways in which meso-level arrangements mediate the relationship between overarching competitive contexts and ethnic conflict. Results of a paired comparative analysis of KKK mobilization in Greensboro and Charlotte demonstrate that social and spatial relations within each city shaped the contours of perceived competition and subsequent ethnic organization in ways that were not always predictable through observation of conventional proxies of competition. (shrink)