On September 30, Russia sent a hard-to-ignore warning to the North Atlantic Alliance. In a letter addressed to Brussels, Moscow stressed that any attempt to isolate Kaliningrad, the Russian exclave in the Baltic Sea, could push it to make use of “the full arsenal of forces and capabilities at its disposal, including nuclear weapons.” The document accused NATO of pursuing a “dangerous and imprudent” course and warned of the risk of a direct armed conflict, even contemplating attacks on allied decision centers from the early stages of a potential escalation. The following day, Russian President Vladimir Putin made the same message public at the Valdai Forum: if Kaliningrad or any other Russian territory were to be hit directly, the question of resorting to all available weapons would move “inevitably and immediately” onto the agenda. The sequence is the usual one: private warning, public signal, and a recurring narrative.
This warning fits a trend that began years ago and sharpened with the 2024 revision of Russia’s nuclear doctrine. The novelty does not lie merely in broadening the premises under which the atomic option could be considered. It also consists in making the nuclear risk much more present in any Western calculation about a possible escalation. In this case, it is necessary to convince the adversary that Russia intends to wage a nuclear war. All it takes is to remind them that certain decisions can trigger a sequence of measures and countermeasures whose outcome is difficult to control. It is Schelling’s old logic: press the adversary by raising the risk, but without necessarily leading to direct confrontation. Applied to Ukraine, it means moving constantly close to certain thresholds, in a war that is nearing five years old, forcing all parties to calculate what they can do, how far they can go and what response each step might provoke.
“It’s Schelling’s old logic: press the adversary by raising the risk, but without necessarily reaching direct confrontation”
What is interesting is that, while Moscow keeps recalling more explicitly the limits of how far escalation can go, it is also increasing pressure at the lower end. Since 2022, gray-zone actions in Europe have intensified and diversified: sabotage, cyberattacks, arson, interference, aerial incursions, and covert operations whose attribution, intent and severity vary greatly from case to case. Not all of them follow a single logic, and it cannot be automatically claimed that Russia is responsible for every incident on European soil. Yet, given their frequency and considering the chosen objectives and the growing use of means capable of causing physical damage, this is a strategic problem that is hard to confine to isolated episodes. Taken together, they allow testing allied responses and injecting uncertainty into Western calculations.
The attempted attack on Leipzig airport is, probably, the recent case that best illustrates this dynamic. In August a drone loaded with explosives appeared there. This airport is one of Europe’s major logistical hubs and plays a significant role in moving military material. After several weeks of investigation, Berlin attributed the operation to Russia, which denied any responsibility. Beyond the particular episode, the case demonstrates how a limited and ambiguous action, far below a conventional military assault, can be directed against infrastructures essential to sustaining Ukraine.
Something similar happens underwater. In spring, British, Norwegian and American forces detected near Svalbard an operation by the Russian unit specialized in deep-sea submarine operations, connected to capabilities aimed at disrupting submarine cables. The operation was intercepted before any sabotage occurred, but it is meaningful because it shows Russia’s interest in possessing means capable of affecting critical infrastructure without triggering an open confrontation.
Seen separately, these episodes can be treated as technical, police or intelligence problems. But what happens when they accumulate? The gray zone expands and shifts from a simple catalog of instruments to functioning as an escalation regime: it fragments coercion and keeps each action below the level that would facilitate a decisive response, while the whole gradually alters the situation.
“These episodes can be treated as technical, police or intelligence problems. But what happens when they accumulate?”
This logic also offers another advantage. To respond, one must detect the incident, investigate it, attribute it, and then decide who responds, how and with what intensity. All of this takes time and, when the political response finally arrives, the operation has usually ended. In the meantime, each action may have revealed information about sensors, reaction times, protocols or tolerances. This tests the adversary and yields learning from its response without offering a clear aim that would justify an escalation.
There is also a shift in the geography of this competition. The European rear is now part of the effort to sustain the war in Ukraine: here weapons are produced, personnel are trained, ammunition is stored, and a large share of the resources reaching the front are moved. Airports, ports, railways, factories, power grids, cables beneath the sea and communication nodes acquire a growing strategic value and, with it, greater exposure to Russian pressure.
That is why escalation in the gray zone does not have to lead to a conventional attack on an ally. There is a broad intermediate space. A campaign of drones against critical infrastructures, combined with electronic interference, cyber operations or sabotage, could serve to pressure European governments, undermine the continuity of their support for Ukraine and create internal costs, all without resorting to an outright military aggression on allied territory. No public evidence that Moscow has decided to take that step, but there is evidence of a dynamic pointing in that direction: gradually shifting pressure from the Ukrainian front toward the European means that enable sustaining it.
Here the link with nuclear coercion becomes visible. It is not necessary to suppose the existence of a master plan coordinating every sabotage, every drone flight and every atomic threat. The chains of command and the actors may differ, but what matters is the overall effect. At the upper end of the spectrum, Moscow tries to make clear how far escalation can go. At the lower end, by contrast, it exploits ambiguity about attribution, intent and the proportionality of the response. Between these two extremes lies Western political decision-making.
“At the upper end of the spectrum, Moscow tries to make clear how far escalation can go. At the lower end, by contrast, it exploits ambiguity about attribution, intent and the proportionality of the response”
The nuclear signaling introduces caution into any decision to escalate, while the gray zone thrives on uncertainty about when a stronger response is necessary. The former introduces prudence; the latter exploits it. That does not mean the nuclear threat grants Russia a veto. Since 2022, the West has repeatedly crossed lines that Moscow had presented as potentially escalating, ranging from the deployment of increasingly advanced systems to the admission of Finland and Sweden into NATO. Nuclear coercion has conditioned the pace and debates, but it has not dictated Western decisions.
The allied reaction to the latest nuclear warning mirrors that balance. NATO rejected the Russian threats, underscored their defensive nature and maintained that there is no imminent conventional threat to allied territory. At the same time, it is strengthening defenses against drones, sabotage and threats to critical infrastructure. The question is not to ignore the nuclear risk, but to prevent its mere invocation from shaping the Western response.
The European challenge also does not rest on deciding whether every drone, fire or sabotage constitutes a casus belli. The issue is to recognize when a sequence of limited actions ceases to be a simple sum of incidents and begins to alter the nature of the confrontation. To do this, it is necessary to identify patterns, accelerate attribution and have graduated responses that allow imposing costs without having to choose between inaction and a disproportionate escalation. That is one of the paradoxes of escalation management: the more the gray zone is exploited to compete below open war, the greater the risk of eroding the very thresholds that should contain the confrontation.
“The question is to recognize when a succession of limited actions ceases to be a mere sum of incidents and begins to modify the nature of the confrontation”
The nuclear shadow and the gray zone are therefore not separate problems. The former raises the perceived cost of escalation; the latter makes it harder to determine when to do so. Together they broaden the space in which Moscow can test limits and impose costs without necessarily provoking an open military response. The allied challenge is to prevent prudence — essential when facing a nuclear power — from turning into paralysis. Because Russia’s advantage does not lie necessarily in erasing thresholds, but in making it increasingly difficult to know when they have been crossed.
