While previous studies of ethnic contention and conflict identify important structural and meso-level indicators of threat and competition, analysis of variation in the mechanisms linking these sources of potential grievance formation with mobilization remains unclear. To address this issue, this study explores the social organization of Ku Klux Klan mobilization in 1960s North Carolina. While regarded as a progressive state in the civil rights era, North Carolina exhibited a greater level of Klan mobilization than the rest of the South combined. We build on models of "mediated competition," where ethnic competition and group threat are held as necessary, and propinquity, authority work, and legacies of previous racial violence link threat and competition with mobilization. Extending prior formulations centered on the discrete impact of individual components of competition, we employ fuzzy-set qualitative comparative analysis to precisely specify the conjunctural conditions governing two modes of Klan mobilization: public rally events and the establishment of local organizational units. Our findings indicate that the mobilizing effects of threat and competition varied between rural and urban areas, and that threat/competition and organization/leadership play a dual role in translating collective grievances into mobilization. K E Y W O R D S : vigilantism; social movements; racism; power relations; minority groups. Theories of ethnic competition and conflict emphasize the motivating role of threat in producing collective action intended to preserve in-group resources and status-quo power relations (Blalock 1957, 1967). Such approaches have broad purchase, and have been compellingly applied to a gamut of contentious outcomes, including ethnic identification and the hardening of divisive attitudes (Coenders