In January, amid Russia’s continued assault on Ukraine and U.S. President Donald Trump’s haste to reach a peace settlement, the leaders of more than two dozen European countries and Canada gathered in Paris to discuss security guarantees for Kyiv. Although European leaders hailed this “coalition of the willing” summit as a breakthrough, its publicly known outcome was a frustratingly familiar, if slightly more detailed, repetition of previous commitments.

The coalition’s signature idea is a multinational European-led force that will deploy to Ukraine if a cease-fire is reached. Planning for this force, which will include land, sea, and air components, is already underway among European militaries and defense ministries, with a headquarters set up near Paris. The force’s mission is twofold: to “support the rebuilding of Ukraine’s armed forces and support deterrence.” Ukraine’s European partners are also discussing a set of binding commitments modeled after NATO’s Article 5 guarantees to come to the country’s defense if it were attacked again after a cease-fire.

The discussions have prompted a sober-minded evaluation of what will be required to deter Russia and convince war-weary Ukrainians that a cease-fire will last. But the guarantees for Ukraine under discussion depend on two contingencies that Europe does not control: sustained U.S. backing and Russian acquiescence.

With or without a cease-fire, Kyiv and its partners need a concrete plan to build up and sustain Ukraine’s military strength. Troop deployments and postwar commitments to act in the event of another invasion will be useful components of such a plan, but they should support what will be the crux of long-term deterrence: Ukraine’s own combat capabilities and defense technological prowess. Kyiv needs a program of partner support that combines major aid packages, investments, acquisitions, intelligence cooperation, and training pipelines as part of a larger plan to strengthen its armed forces and industrial base—ideally an effort that will continue for at least five years.

The price tag for underwriting Ukrainian rearmament will be steep, and Europeans have struggled so far to provide the funds required for long-term planning. But the alternative—a Ukrainian military perpetually in survival mode—would be far costlier. If Europe is as serious about preventing Ukraine’s defeat as it now appears to be, a coordinated long-term strategy will do more to help Kyiv, not to mention signal Western resolve, than its current practice of lurching from one aid package to another.

Ukrainians often warn Western leaders against repeating the mistakes of the Budapest Memorandum, the 1994 agreement under which Russia, the United Kingdom, and the United States agreed to respect Ukraine’s borders in exchange for the surrender of the nuclear arsenal Ukraine inherited from the Soviet Union. Although Ukrainian leaders in subsequent decades let the country’s armed forces fall into disrepair, the vague and unenforceable memorandum has nonetheless become shorthand in Ukraine for the empty promises that made Russia’s 2022 full-scale invasion possible.

Today’s discussions among Europeans, Americans, and Ukrainians, however, are far removed from those of the early 1990s. The once-implausible idea that Western governments would ship hundreds of billions of dollars in advanced military equipment to Ukraine has become the baseline for Kyiv and its partners.

The Trump administration has signaled that it is open to participating in a security framework for Ukraine that includes both a European-led troop deployment and so-called Article 5–style guarantees. European leaders are angling for Trump’s agreement to use U.S. intelligence, logistics, and command capabilities to support the multinational force, which European nations would have a hard time deploying on their own, as well as to backstop it if Ukraine comes under attack. Europe and Ukraine are convinced, with good reason, that any guarantee lacking U.S. backing stands little chance of being taken seriously by Moscow. Europe lacks Washington’s record of making and enforcing guarantees on its own: since the end of World War II, European leaders have conducted defense policy largely within U.S.-led frameworks such as NATO, in which Washington ultimately manages escalation and warfighting.

Yet even with U.S. involvement, the credibility of European guarantees would remain uncertain. NATO and U.S. defense guarantees in Asia, two models for successful deterrence, are less functions of finely tuned treaty language than of decades of integrated planning, joint exercises, high-level consultations, and the persistent presence of combat-capable U.S. troops. Simply put, any would-be aggressor understands that an attack on a treaty ally of the United States would invite a U.S. military........

© Foreign Affairs