This article uses a structural approach to the investigation of the continuity and discontinuity between ‘old’ urban and ‘new’ environmental protest, opening further space for analysis of the relationship between different mobilizations in Northern Ireland. In particular, I suggest that the ‘novelty’ and strength of social movements’ challenges can be assessed in terms of their capacity to promote participation and cooperation between the opposite poles of established cleavages, especially when one engages in the analysis of socio‐politically polarized contexts. In this article I focus on two mobilizations. On the one hand, I show that the first Westlink protest of the 1970s was not the product of an integrated social movement but, rather, of a heterogeneous and instrumental coalition of urban and political actors which gained no support from formal environmental organizations and soon split along the national‐religious divide. On the other hand, I show that the current Westlink campaign is the product of a cohesive network, which cuts across the many socio‐political cleavages of Northern Ireland, linking together local, urban and community groups, conservation and environmental organizations, associations, universities, political actors and parties, of opposing national‐religious identity. I then take these two patterns of mobilization as a dependent variable and explain them by drawing on theories of resource mobilization, new social movements, framing and political opportunity structure.