This working paper authored by researchers from the Stiftung Wissenschaft und Politik (SWP) and the Peace Research Center Prague presents a comprehensive, data-driven chronology of nuclear signaling in the context of Russia’s war against Ukraine during the Biden administration, covering the period from autumn 2021 through January 2025. It systematically documents and analyzes public statements and observable actions by Russia (and Belarus) as well as responses by the United States and key NATO allies, with the aim of tracing how nuclear-related signaling evolved alongside the war and Western support for Ukraine.
The paper begins with key nuclear-related developments and a graphic overview of signaling trends, followed by detailed monthly sections that track statements and actions from the pre-invasion phase through successive stages of the conflict.
In total, the authors identified, evaluated, and coded over 400 nuclear-relevant statements and actions. These were coded using an inductively developed taxonomy of Nuclear Escalation Relevant Signals (NERS), comprising eight categories for Russia and eight for the West.
The main results of the coding show a pronounced asymmetry. Most Russian signals fall into the category of nuclear escalation-risk signaling, i.e. statements designed less as explicit threats and more to amplify perceptions of uncontrollable nuclear risk. By contrast, Western signaling is dominated by efforts to deter Russian nuclear use, reinforce norms of non-use, and de-escalate tensions, while largely avoiding explicit nuclear threats of its own.
The central takeaway of the report is that nuclear weapons played a persistent but largely indirect role in the war: Russia’s nuclear signaling shaped Western risk perceptions and decision-making without producing direct nuclear escalation, while Western restraint and escalation management limited the coercive effectiveness of these threats. By grounding debates on nuclear deterrence, coercion, and escalation management in a systematic empirical record, the paper provides a foundation for more cumulative, evidence-based research on nuclear risks in contemporary great-power conflicts.