What roles do cities play in fostering general social movements? This article maintains that cities facilitate particular types of relations that are good at making high‐quality resources available to mobilizations operating at a variety of spatial scales. However, while large and complex urban systems may be well suited for these types of relations, whether they actually develop depends on the nature of local power relations between political authorities and civic organizations. In certain cities local configurations of political power may favor the growth of these relations, with these cities becoming important nodal points in geographically extended social movement networks. In other cities, by contrast, local configurations of political power may hamper the formation of these relations. This is a theoretical article that draws on network theory to inform the conceptual framework and a variety of empirical cases for illustrative purposes.