Despite years of ongoing interventions by multiple external and regional actors, the security situation in west Africa's Sahel region is dramatically deteriorating. In this introduction to the special section of the July 2020 issue of International Affairs, we zoom in on four major external international intervention actors (France, the United States, the European Union and the United Nations) in the Sahel region's escalating 'security traffic jam'. We argue that the diversity of intervention actors makes the Sahel a paradigmatic case for exploring a set of often-overlooked constitutive intervention effects. By adding new temporal, relational and spatial dimensions to the notion of 'constitutive effects' as introduced by post-structuralists in the 1990s, we (re)launch constitutive effects as a conceptual framework for approaching the study of ongoing intervention engagements. From this perspective, and as further illustrated in this special section, intervention continuity and escalation cannot be explained simply with reference to frameworks of 'success' or 'failure', but require a broader conceptualization of effects, including how specific threat perceptions, rationales and problematizations get constituted and consolidated through and during ongoing intervention practice. Contributions to this special section each unpack a diverse set of constitutive effects including the contested performance of security actorness, the (un)making of security alliances and partnerships, logics of choices produced by ongoing intervention practices, as well as the constitution of conditions for continual international involvement.