Social movement researchers recognize the importance of brokerage for the spread of contentious politics. This study proposes a new classification of brokerage and identifies the main types of brokers depending on the subgroups to which actors belong and on the subgroups' miscibility. It also introduces the "diffusion and scale-shift paradox": contention spreads more quickly when brokers connect few groups and when they connect groups that are highly miscible; yet, contention cannot spread widely if brokers do not connect diverse groups and groups with low miscibility. The empirical analysis compares the spread of contention on the issues of peace and civil liberties. Results support the scale-shift paradox—they show that contention on civil liberties diffused to more municipalities and shifted upwards to more states mainly because civil liberty activists built bridges between groups that were at opposite ends of the ideological spectrum and outside the progressive community.

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