In 2022, when Russia launched its full-scale war in Ukraine, the Kremlin’s strategic thinking was shaped around several core ideas. It viewed the United States as its principal geopolitical rival, an adversary that had encouraged Kyiv to impose strategic defeat on Moscow. It considered Europe and NATO largely as an extension of American power. And it saw nuclear muscle flexing as efficient means to exert coercive pressure.

Today, after nearly five years of war, and 22 months of the second Trump administration, the mental map guiding Russian strategy has changed. First, Russia now sees Europe, instead of the United States, as its principal geopolitical adversary, a shift that has driven Russia’s defense establishment to call for an approach known as “castling” to deal with the main threats. Related to this, Moscow now attributes new strategic agency to Europe itself because of the dramatic military modernization taking place in many European countries and the growing interest among some European leaders in developing or extending their own nuclear deterrent. A third shift concerns Russia’s theory of deterrence: Moscow’s traditional understanding of nuclear coercion is giving way to new thinking about nonnuclear strategic deterrence using advanced conventional weapons systems aimed at Europe.

These new lines of thought, which have gained prominence among influential defense intellectuals and policy experts close to the Kremlin over the past year do not need to be endorsed in formal security doctrine to matter. As the past decade has shown, ideas circulating within Russia’s national security establishment have shaped how officials frame problems, define options, and ultimately make major strategic choices. The three recent shifts in Russian strategic thinking will likely play an important part in how Moscow approaches any negotiation to end the war, as well as how it manages future escalation and competition with Europe and the United States.

As the Trump administration steps up its efforts to engage Moscow, it is now negotiating with a Russian leadership whose strategic mindset has evolved considerably since 2022. For the United States, understanding Russia’s new mental map will not only be crucial to any attempt to find an off-ramp with Moscow. It will be also be essential to reducing the risk of inadvertent escalation between Russia and Europe and to ensuring strategic stability on the continent in the years to come.

One of the most notable trends in Russian strategic thought over the past year has been the emergence of the idea of “castling.” A term borrowed from chess, castling in geopolitics describes the repositioning of forces and resources to optimize a state’s strategic posture. Moscow’s defense experts have used the concept to describe a strategy for dealing with a new reality: for the first time since World War II, they have argued, Europe, rather than the United States, has become Russia’s principal geopolitical adversary. According to this view, European countries are now the principal source of Ukraine’s military capacity, political resolve, and strategic resilience; it is Europe and not the United States that has made Ukraine its proxy and is encouraging Kyiv to pursue Moscow’s strategic defeat.

As a consequence, Moscow must direct coercive pressure at Europe—its elites, its decision-making centers, and its critical infrastructure. By doing so, Russia can instill into Europe’s calculus what theorists in Moscow call a “deterring fear”: a European reluctance to antagonize Russia through further support to Ukraine. Such action, they argue, can also rebuild Russian credible deterrence for long-term competition with the West, which is now centered on Europe.

Castling does not imply a change in Russia’s overall objectives, which remain........

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