Multiplexity and strategic alliances: The relational embeddedness of coalitions in social movement organisational fields

• Alliance is heavily embedded suggesting cost minimisation is a dyadic aspect of its formation.
• SMOs may pool allies and entrained resources without establishing alliances with others.
• Alliance is structurally embedded in multiplex triadic configurations of expressive ties.
• Uncertainty reduction vis-à-vis identity governs alliance formation in the presence of positive nomination.
• Micro–macro integration of organisational fields is a function of multilevel and multiplex dynamics.

While scholars have embraced the notion of social movements as networks, there has been little empirical exploration of the emergence of coalitions within these multilayered systems. Here I explore the role of overlapping relations in alliance formation amongst a group of 55 health-related professional social movement organisations mobilised against austerity. Using cross-sectional bivariate exponential random graph models, I find dependencies between digital proxies for alliance, shared allies, information exchange, positive nomination and offline colobbying activity at the dyadic, degree and triadic levels. Cross-network associations indicate that multiplexity plays a non-trivial role in the formation of alliances and, more generally, social movement organisational fields, necessitating increased attention from scholars of social movements.