For Ukraine, the most dangerous moment in a war is often the moment when the fighting appears to stop.
A ceasefire can look like peace. In reality, it can be a pause. Ukraine learned that lesson once already.
The lesson of Minsk
The Minsk agreements were supposed to freeze the war in Donbas. Instead, they gave Russia eight years to rebuild its army, deepen its influence in occupied territory, and prepare the full-scale invasion of 2022.
That experience is the reason Ukraine cannot demobilize after any new ceasefire.
The question is whether Europe can reinforce Ukrainian deterrence—and how.
Any serious post-war settlement already assumes this. In December 2025, European leaders meeting in Berlin outlined the requirements for credible security guarantees for Ukraine. Central to their proposal was that Ukraine retain an army of roughly 800,000 personnel even in peacetime—enough to deter renewed Russian aggression.
That is the real security guarantee.
Diplomatic commitments may reinforce deterrence, but they cannot replace it. Ukraine’s army will remain the primary barrier against a second invasion. The question, therefore, is not whether Western security guarantees are fully credible. The question is whether Europe can reinforce Ukrainian deterrence—and how.
Enter the E5
The emerging answer is the so-called “E5.”
The E5—France, the United Kingdom, Germany, Italy, and Poland—has become the core political forum for coordinating Europe’s response to the war. These five states collectively represent most of the European Union’s military and industrial capacity.
Poland is rapidly expanding its armed forces into one of the largest land armies on the continent.
Britain and France are nuclear powers. Germany is Europe’s largest economy and is rearming after decades of underinvestment. Poland is rapidly expanding its armed forces into one of the largest land armies on the continent.
Together, they have the potential to form the backbone of a European security guarantee for Ukraine.
At the Berlin talks in December 2025, leaders proposed a European-led multinational force that could operate inside Ukraine after a ceasefire—helping regenerate Ukrainian military capabilities, securing Ukrainian airspace, and supporting maritime security in the Black Sea.
President Emmanuel Macron has spoken of establishing military hubs across Ukraine.
German Chancellor Friedrich Merz went further, saying that under such guarantees Western forces might ultimately be required to repel Russian incursions if Moscow violated a ceasefire. President Emmanuel Macron has spoken of establishing military hubs across Ukraine and building protected facilities to support Ukrainian forces after any agreement.
The model envisioned: Ukraine maintains a powerful national army, while European partners provide additional deterrence through training missions, operational support, and limited troop deployments.
The American question
But the structure still has a major gap: the United States.
For decades, European security rested on American leadership through NATO. The emerging architecture for Ukraine reflects growing uncertainty about that assumption. European leaders are increasingly preparing for a scenario in which Washington’s role becomes less predictable—whether because of domestic politics or competing global crises.
The EU’s “Readiness 2030” program, designed to mobilize hundreds of billions of euros for European military capabilities, reflects precisely that concern.
Participation in any military response would ultimately remain a national decision for each government.
In practice, the E5 may become the operational center of European deterrence for Ukraine. But the E5 is not NATO. It has no treaty obligation equivalent to Article 5, no permanent command structure, and no mechanism that automatically commits its members to respond.
Participation in any military response would ultimately remain a national decision for each government—subject to domestic politics, constitutional constraints, and the mood of the moment.
The goal, as European Commission President Ursula von der Leyen has described it, is to turn Ukraine into a “steel porcupine”.
An aggressor that senses hesitation will probe it. That is what makes Ukrainian military strength the decisive factor, not a supplement to external guarantees but the foundation beneath them.
European leaders increasingly frame Ukraine’s future defense in exactly those terms. The goal, as European Commission President Ursula von der Leyen has described it, is to turn Ukraine into a “steel porcupine”—a country so heavily armed that renewed invasion becomes prohibitively costly. European deployments can support that strategy. Training missions can strengthen it. Industrial cooperation can sustain it.
Above that sits the wider political backing of the United States and NATO partners, even if their military role becomes less direct.
The most realistic post-war security architecture is layered. At the center stands Ukraine’s own army—large, experienced, and permanently mobilized.
Around it sits a network of European support: training missions, intelligence sharing, defense-industrial integration, and potentially multinational forces deployed in limited numbers on Ukrainian territory. Above that sits the wider political backing of the United States and NATO partners, even if their military role becomes less direct.
This may not resemble NATO membership. But it could still produce a powerful deterrent if its components reinforce each other.
The only guarantee that holds
The alternative is familiar. If Ukraine demobilizes after a ceasefire while security guarantees remain politically ambiguous, Moscow gains what it exploited after Minsk: time. Time to rebuild its forces. Time to adapt its strategy. Time to prepare the next war.
The foundation will be the same as it has always been—the strength of her own army.
Ukraine must remain armed. Security guarantees may strengthen deterrence. European deployments may reinforce it. Political commitments may help sustain it.
But the foundation will be the same as it has always been—the strength of her own army.
On paper, security guarantees are easy to write. On the battlefield, they must be earned.
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