In their discussions about ending the war in Ukraine, Americans and Europeans are increasingly focused on providing Kyiv with security guarantees. After over a decade of conflict with Russia, including four years of all-out war, Ukraine understandably does not trust Moscow to abide by any cease-fire. Before Kyiv signs one, it wants assurances from its key partners that if Russia attacks again, Ukraine will not be left to fend for itself.
To meet this demand, some allies have suggested giving Ukraine assurances modeled on NATO’s Article 5, which declares that an attack on one NATO country is an attack on all. Others have recommended stationing European troops in the country as a way to give such assurances teeth. But these proposals lack credibility. NATO allies have steadfastly refused to intervene directly in the current war, so any promise they make to fight Russia in a new one is simply not believable. The Kremlin knows this better than anyone, and such bluffs will not deter it.
American and European leaders can provide Ukraine with a real postwar guarantee. But to do so, they will have to stick to promises that are credible. And that means committing to a more intense version of their current behavior in the event that Russia violates a cease-fire deal. In other words, should Moscow attack Ukraine again, the country’s allies would reimpose sanctions on Russia, provide new financial support to Kyiv, and offer Ukraine military assistance that goes beyond what they would offer in peacetime. The United States and its allies would codify these pledges into law and create mechanisms that activate them if Russia attacks.
These guarantees, of course, fall short of an Article 5–like pledge. But if combined with peacetime measures that strengthen the Ukrainian military (which will remain Kyiv’s primary source of deterrence), they will still affect the Kremlin’s calculus. The United States and Europe, then, can help ensure that any renewed aggression is prohibitively costly for Russia, even without directly intervening.
CREDIBILITY AND CREDULITY
NATO countries have made enormous efforts to help Kyiv resist Moscow’s invasion since it began February 2022. Among many other steps, they have levied progressively harsher sanctions on Russia, supplied Ukraine with vital intelligence, and given it sophisticated weapons (including air defenses). But they have consistently declared that they are not willing to go to war with a nuclear power over Ukraine and have refused to send troops. They have also declined to offer Kyiv membership in NATO. And they will not let Ukraine use their weapons in ways that they believe might drag them directly into the fight.
New pledges by a few European countries to deploy troops to Ukraine after a cease-fire agreement might suggest that this approach is shifting. But any “reassurance forces,” as the continent’s leaders call them, are unlikely to amount to much. Europe has refused to fight Moscow on Kyiv’s behalf in this war, because it is not in the continent’s core national security interests to do so. European publics also consistently oppose direct intervention. A deployment of forces after a cease-fire will not alter these realities. If France, the United Kingdom, or any other countries send troops and they come under Russian attack, they might well catch the next train out.
The United States and Europe are not prepared to fight on Ukraine’s behalf. Yet they are clearly willing to slap sanctions on Russia and provide Kyiv with offensive arms, financial support, and intelligence. The bilateral security agreements signed in 2024 between Ukraine and its key international partners have already committed multiple NATO members (including Washington) to consistently supply such assistance, both during the war and after it ends. But Ukraine also needs a promise that its partners will dramatically surge support in the event of future Russian aggression, and a structured process to ensure they make good on that pledge. The country’s guarantors must signal to Moscow that renewed aggression will be met not just with Ukrainian resistance but with a massive intensification of external support.
NATO allies are not willing to go to war with Russia on behalf of Ukraine.
Sanctions are the most immediate instrument. As part of any negotiated settlement with Moscow, the United States and Europe will likely agree to relieve some of their economic restrictions. But if Moscow violates the deal, they must again kick Russian banks out of SWIFT (the Europe-based international banking transfer messaging system). They must also reimpose full export controls on dual-use and high-tech goods, renewed bans on its sovereign debt and energy investments, and strict price caps on its oil exports. Ukraine’s allies could also pile on sanctions in escalating tiers should Russia continue its aggression. The first tier might freeze any Russian assets held abroad; the second could extend sanctions to shipping, insurance, and commodity trading; and another could impose secondary sanctions on entities in third countries, particularly those enabling Russia’s war economy through oil and gas purchases (something that Washington and Europe have not been willing to do in the current war).
Sanctions alone, of course, cannot stop Russia’s tanks. For that, Ukraine will need more weaponry. If Moscow agrees to a cease-fire, the United States and Europe would shift away from flooding Ukraine with offensive arms and provide it with weapons that enable a porcupine type of defense-oriented strategy that incorporates air defenses, antitank systems, and drones. If Russia violates the settlement, however, Kyiv’s partners would quickly increase the flow of offensive assistance. They will need to pump the country full of longer-range missiles, such as army tactical missile system (ATACMS) from the United States and Storm Shadows from France and the United Kingdom. They will have to accelerate deliveries of combat aircraft, armor, long-range strike drones, and artillery. And they will need to remove current range restrictions and authorize Kyiv to use donated systems against military targets inside Russia, provided those targets are directly linked to the invasion. The sharing of intelligence for targeting Russian forces, suspended in peacetime, would resume.
The last instrument of a credible security guarantee is financial help. War, after all, is as much a test of economic stamina as it is of battlefield performance, and Ukraine will need monetary assistance to stay afloat while fighting. The G-7 states should thus set up a standing Ukraine stabilization fund that can surge aid to Kyiv. If Russia and Ukraine are at peace, the fund would pay for Ukraine’s reconstruction and offer macroeconomic assistance. But if Russia resumes its attacks, the fund would disperse large-scale budgetary support and finance military production, allowing Ukraine to keep fighting as long as necessary.
MONEY-BACK GUARANTEE
After Russia’s full-scale invasion, outside aid to Ukraine was discretionary and often delayed, subject to long political debates. To be effective, these security guarantees cannot be similarly unstable. Instead, they must be applied quickly and automatically. Ukraine’s guarantors should therefore set up a clear framework, agreed-on triggers, and financial and legal mechanisms that ensure each state meets its commitments.
Ukraine’s allies can accomplish this by codifying some of their commitments into law. Washington, for example, could pass legislation that triggers automatic sanctions against Russia and provides funds for Ukraine in case of renewed Russian aggression. The European Council should enact a similar mechanism. The EU usually requires unanimity to impose sanctions. But there are workarounds—namely, the body’s qualified majority clauses—that EU member states can use to reimpose restrictions.
The process of triggering these guarantees should be fast and direct. If Kyiv charges Moscow with violating the cease-fire, the guarantors’ foreign ministers should meet within 48 hours to examine Ukraine’s claims and pore over intelligence from a variety of sources. Yet unless a majority of the guaranteeing states decide Ukraine is wrong, the snapback must take effect. This system may afford substantial power to Kyiv, but flipping the burden of proof is essential to deterring the Kremlin. Otherwise, Russia might salami-slice its way across the cease-fire line without triggering consequences.
To make sure that Ukraine quickly receives the military support it will need in the event of a renewed Russian assault, the United States and Europe should sign standing contracts with their defense industries to produce the long-range missiles, advanced aircraft, artillery systems, and other weapons necessary to support Kyiv. Ukraine’s partners should also pre-position munitions in designated stockpiles in bordering states’ territory. Likewise, NATO should make sure training centers in Germany, Poland, and the United Kingdom always have room for Ukrainian troops, in case the war resumes and Kyiv needs to get its reserves into fighting shape.
Finally, the United States and Europe must review this system regularly. They should publish a joint report on the state of Ukraine’s security, the health of the guarantees, and the readiness of snapback mechanisms once each year. Parliamentary committees in the U.S. Congress, the European Parliament, and various national European legislatures should hold hearings of their own, too. Doing so will help ensure that this system retains its democratic legitimacy—and thus its support.
WHAT IS AND WHAT WILL NEVER BE
A security guarantee based on snapback of sanctions, financing, and weapons may not have the grandeur of NATO’s Article 5 or the bravado of deploying European forces to Ukraine. But for Kyiv, those are illusions, not real options. Ukrainians should not rely on the United States and Europe to do something in the future that they have repeatedly refused to do for the last ten-plus years.
These measures, by contrast, are credible precisely because NATO has already demonstrated its willingness to take them. They can, in other words, give Ukraine confidence that it will not be abandoned—without inspiring false hope. They can make clear to Russia that an attack will bring automatic punishment. And together with Ukraine’s own formidable armed forces (and peacetime provisions of military aid), they can deter the Kremlin and ensure an enduring peace.