Coalitions are becoming more prominent in some social movement arenas, but little is known about how the presence of coalitions influences movement development. Social movement research and organization ecology provide contrasting perspectives on coalitions, viewing them as cooperative and competitive organizational strategies respectively. Drawing on social movement and organization ecology theses, I suggest that the increasing number of coalitions in recent social movements may be a double-edged sword in terms of movement growth, enhancing the position of existing movement actors while discouraging the formation of new organizations. With their unique access to the shared resources of the collectivity, coalitions can consolidate the position of existing groups and inhibit new organization formation in a competitive organizational field.

I evaluate the role that coalitions play in the development of the transnational environmental movement by examining the relative contribution of environment, legitimacy and competition within and between movement organizations to movement development. I conclude that coalitions proliferate in response to competition among other organizations, but that coalition growth then reduces the number of new organizations entering a population. Coalitions play a vital role in shaping movement trajectories, a function that is largely ignored in the current literature.