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This is a hypothetical scenario, but not a far-fetched one: undisclosed intelligence assessments reportedly circulated in early summer 2026 warned of possible Russian provocations, including a limited armed attack on Polish territory. Since Russia’s full-scale invasion of Ukraine in February 2022, European states have significantly strengthened their military preparedness. Defence spending among EU member states has risen from €197 billion annually in 2015 to €454 billion in 2026.

Yet the scenario above exposes different but equally important vulnerabilities that have received far less attention: the need for a shared situational picture, common principles to guide crisis responses, and institutions and networks that can be effectively mobilised.

First, the situational picture. While NATO prepares for a wide spectrum of aggression scenarios, developing a shared situational picture among 32 allies, or even the EU’s 27 member states, remains a political exercise. In the event of a Russian drone strike, the immediate challenge would be determining whether it can be confirmed that the drone was Russian and whether the incident constituted an attack on NATO territory. Attribution alone could take time, as recent drone incursions and cable sabotage across Europe have shown.

Strategic thinking in an increasingly contested international environment requires clarity about one’s own objectives and values.

The ability to interpret an attack collectively rests on a shared conception of European security. Europe has long pursued greater convergence in threat perceptions and strategic assessments. This has become increasingly urgent, as Europe can no longer assume that the US will provide the political leadership in framing an incident as a violation of European states’ sovereignty when it is one.

Second, principles. Crises test the common principles on which collective action depends. In a crisis like a Russian drone strike, Europeans would likely refer to international law to condemn the attack, justify a response and mobilise international support. NATO’s commitment to defend every inch of allied territory would also be cited.

The problem is that Europe’s own commitment to shared principles has raised concerns. Earlier this year, European responses to the US use of force against Iran left everyone confused about where Europe stands. The US was disappointed by the lack of meaningful European backing, while observers in the Global South interpreted Europe’s silence as evidence that it defends international law selectively.

Europe’s principles remain ambiguous and their application compartmentalised. Governments tend to focus on the immediate pressure of adopting an acceptable position, paying less attention to how today’s decisions affect Europe’s credibility and room for manoeuvre in future crises. Strategic thinking in an increasingly contested international environment requires clarity about one’s own objectives and values.

Third, institutions. An effective crisis response depends not only on capabilities but also on institutions able to manage and coordinate them despite shifting political realities. Much attention has been devoted to the consequences of a declining US role in NATO, but an equally important question is how a more European NATO is beginning to operate. Similarly, the EU must be able to function in crises, not least to provide financial backing for a member state under attack. But as things stand, a single opposing member state could halt EU decisionmaking even during a Russian attack.

European defence arrangements are becoming more differentiated, relying on national capabilities and regional frameworks. This offers opportunities: in crisis scenarios, regional groups can provide initial political coordination and military reinforcement, helping to prevent hesitation at the alliance level from turning into paralysis. In the event of an armed attack, Poland might also invoke the EU’s mutual assistance clause to mobilise broader political and military support.

Much attention has been devoted to the consequences of a declining US role in NATO, but an equally important question is how a more European NATO is beginning to operate.

Yet there is an urgent need to ensure that this differentiation does not become fragmentation that would obscure responsibilities in scenarios like the one above. Regional and minilateral initiatives should reinforce NATO’s collective decision-making rather than create competing centres of political authority. Moreover, important questions remain regarding NATO-EU cooperation in a crisis context. Clarifying these issues before a crisis occurs would strengthen Europe’s preparedness.

Fourth, networks. Ukraine’s experience in coping with Russia’s immediate and prolonged aggression offers one particularly important lesson for Europe: defence depends on broad international partnerships capable of rapidly mobilising and sustaining material support as military technologies evolve.

Political attention and resources devoted to European defence risk coming at the expense of broader international partnerships. This is short-term thinking. An alliance backed by extensive international support can insist on defending every inch of its territory, while an isolated alliance has less room for manoeuvre.

The next test of European security may not begin with Russian tanks crossing a NATO border. It may begin with a deliberately ambiguous act that forces Europeans to decide what has happened and what they are prepared to do about it. More weapons can give weight to that decision, but they will not make it for Europe.

European preparedness therefore requires more than rearmament. Europe needs the capacity to understand a crisis collectively, respond according to common principles, mobilise institutions quickly and sustain its response through international partnerships.

Why does this matter now?

Rearmament alone will not ensure Europe can respond to external aggression.

What needs to change?

Europe must shift from crisis management to strategic preparedness. Europe needs shared threat assessments, clear principles, effective institutions and strong international partnerships.

What needs to be done?

Europe should strengthen cooperation between national, NATO and EU assessment and planning bodies, clarify principles for collective action, stress-test how institutions would work together in a crisis, and invest in broad international partnerships that sustain defence.