The danger of nuclear war appears to have been increasingly overlooked in international studies, especially in Europe, despite undiminished risks. If anything, today’s security landscape – marked by multiplying conflicts, shifting alliances, eroded arms control agreements, and blurred lines between conventional and nuclear weapons – has heightened the possibility of catastrophic miscalculation.

This project examines the dynamics of crisis bargaining between nuclear powers and re-evaluates the psychological foundations of deterrence theory, to better understand what motivates nuclear threats and how to respond to them. Specifically, I ask whether states try to make nuclear threats more believable by making them deliberately ambiguous or ‘leaving something to chance.’ This idea, developed by game theorist Thomas Schelling, was a response to the context of ‘mutually assured destruction,’ where a first strike automatically invited an unacceptable response, making the initial threat inherently non-credible. By emphasizing the element of chance over the choice to use nuclear weapons, suggesting their control over the decision was ultimately limited, leaders may want to exploit their adversaries’ fear and risk aversion.

While all nuclear powers employ ambiguity, Russia’s intensified threats during the Ukraine War provide a distinct example of this tactic, especially since its rhetoric is increasingly at odds with doctrine, force posture, and technological developments.

My research explores two puzzles. First, how can ambiguity be integrated into theories of coercion, deterrence, and brinkmanship? Scholars building on the work of Schelling suggested chance emerged mainly from domestic politics, bureaucracy, or organizational flaws, sidelining the role of individual decision-makers. I analyze how leaders strategically employ chance, while the ultimate choice over nuclear escalation remains in their hands. Second, I ask why states avoid categorical ultimatums, instead ‘leaving something to chance.’ While ambiguity enables a more flexible bargaining strategy, overuse can also undermine one’s credibility. Existing frameworks struggle to model escalation processes in the absence of explicit threats.

I investigate pathways used by state actors to leverage chance, while also considering alternative sources of ambiguity emerging by accident. For instance, I explore how states introduce inconsistencies within their nuclear doctrine and strategy, shroud nuclear threats in religious language, or act willfully negligent, increasing accident risks to signal resolve.

By relying on ambiguity to make threats more credible and achieve their objectives, leaders deliberately limit their own control, creating a paradox: rational goals, pursued through irrational means. I suggest that one needs to unpack human emotion – such as the fear of uncontrollable escalation or an adversary acting irrationally – to understand why some threats work, while others don’t, and how to respond.