Forum Choice and Cohesion in NATO’s Response to Russia’s War on Ukraine

The article examines how forum choice shaped NATO cohesion during Russia’s war against Ukraine between 2022 and 2025. It asks under what conditions Allies used NATO rather than minilateral formats, and what effects these choices had on alliance cohesion. Drawing on qualitative case analysis, the article develops a simple forum-choice framework based on four variables: unanimity cost, escalation risk, partner-inclusion needs and operational fit with NATO’s integrated structures. It argues that the main lesson from the War in Ukraine for NATO was that cohesion could be sustained because Allies matched the venue to the task. Collective defence adjacent deterrence, enlargement and industrial target-setting remained within NATO, where legitimacy and operational fit were highest and consensus worth the cost. By contrast, lethal aid, escalation-sensitive capabilities, training, contingency planning and some regional reassurance were channelled through mini-lateral coalitions, which provided speed, variable geometry and inclusion of non- NATO partners while shielding NATO from the most divisive decisions. The article thus reconceptualises mini-lateralism as a cohesion-preserving mechanism within a layered Euro-Atlantic security ecosystem, and brings forum choice into the emerging literature on NATO cohesion.