The debate over security guarantees for Ukraine has moved from abstract diplomacy to concrete instruments. Since the G7’s Vilnius joint declaration in July 2023, which framed long‑term international support for Ukraine as an element of Euro‑Atlantic security, a practical architecture of bilateral and plurilateral commitments has begun to take shape. Those commitments matter because they will define Kyiv’s alignment choices after the war and the balance of deterrence on Europe’s eastern flank.

Between January and March 2024 a cluster of Western and European states signed ten‑year security cooperation agreements with Kyiv. The United Kingdom’s January accord set a model for a binding intergovernmental framework of rapid consultation and sustained military, intelligence and cyber support. France and Germany followed in mid‑February with their own long‑term pacts, pledging multi‑billion euro packages, air‑defence and training commitments and mechanisms for emergency consultations in case of renewed aggression. Denmark and the Netherlands signed similar agreements in late February and early March, broadening the geographic and capability base of Kyiv’s security partners.

These bilateral arrangements reflect two political realities. First, many European states are unwilling or unable to offer Ukraine immediate NATO membership, even as they publicly endorse Kyiv’s Euro‑Atlantic aspiration. Second, governments are ready to craft instruments short of Article 5 that nevertheless commit resources, logistics and political consultation for an extended period. The EU sits between these poles. It is Kyiv’s economic and political anchor through candidacy and deep institutional alignment, but the EU’s legal and treaty architecture does not create automatic collective defence in the way NATO’s Article 5 does. That distinction will shape post‑war alignment calculations.

From a strategic perspective there are four plausible post‑war alignment scenarios to consider.

1) NATO Integration as the End State. This is Kyiv’s declared strategic objective. Full NATO membership would provide the clearest, legally binding deterrent through collective defence. The political obstacles are nevertheless substantial: unresolved territorial occupation complicates accession mechanics, allies would need to accept the geopolitical risks of extending the alliance’s mutual defence clause to frontline Ukraine, and the accession process would be lengthy. Even if this remains the normative goal, NATO accession as an immediate post‑war outcome is the least likely near‑term scenario.

2) A European‑led Security Compact Supplemented by Bilateral Guarantees. In this scenario the EU and willing member states deepen CSDP instruments, pooled procurement, and a standing European training and air‑defence mission tailored to Ukrainian needs, while individual states sustain long‑term bilateral pledges. The bilateral accords seen in early 2024 establish the template for this model: legally framed assistance that endures until NATO membership or for a decade, whichever comes first. Such a hybrid could deliver credible deterrence without immediate NATO expansion, but it depends on sustained political will, predictable financing and interoperability between national forces and any EU framework.

3) A Networked Security Architecture of Plurilateral Pacts. Here Ukraine remains outside NATO, but its defence is underwritten by an evolving web of multilateral agreements among like‑minded states. These pacts would combine intelligence sharing, rapid resupply commitments, sanctions triggers and possible deployment of multinational reassurance forces in non‑contact zones. The G7 declaration’s operational logic points toward this modular approach, which can be politically easier to assemble than unanimous NATO or EU treaty changes but is weaker in legal guarantees and more complex to coordinate.

4) A Limited Settlement and Partial Reintegration into European Structures. The least desirable but plausible outcome for Kyiv is a settlement that freezes parts of the front or accepts de facto separation in exchange for limited international guarantees and reconstruction funding. In that case EU accession momentum—already launched through candidate status—would become the main security and economic anchor, but without the military protection Kyiv seeks. The lessons of the 1994 Budapest assurances remain potent here: political assurances that lack robust enforcement mechanisms leave room for revisionism. Any post‑settlement architecture that omits credible military deterrence risks repeating those mistakes.

Assessing feasibility and risks

Each scenario has trade‑offs. NATO accession delivers the strongest guarantee but risks escalation politics and a prolonged accession calendar. A European security compact could institutionalise defence industrial cooperation and force generation inside the EU but will struggle with unanimity and treaty limits on collective defence. A network of bilateral pacts is agile but legally fragmented and reliant on the strategic cohesion of partners. A limited settlement anchored primarily in EU integration would offer reconstruction and political normalization but minimal military deterrence.

Three structural constraints will determine which of these scenarios becomes dominant. First, the distribution of military capabilities inside Europe. Air defence, long‑range fires and sustainable munitions production matter more than legal formulas. The bilateral agreements signed in early 2024 explicitly prioritized these capabilities, which is no accident. Second, domestic politics in key capitals. Long‑term guarantees require parliamentary consent, budgetary allocations and public backing. Third, the credibility of enforcement mechanisms. Guarantees tied to rapid consultations and automatic sanctions triggers are useful only if they are backed by contingency plans for force posture, logistics and information sharing.

Policy implications for EU leaders

For Brussels and national capitals that want to maximise deterrence while minimising escalation, three priorities are immediate:

1) Convert political pledges into predictable, multi‑year funding lines for air defence, ammunition production and replenishment. The experience of 2022–24 shows that capability sustainment beats one‑off donations.

2) Build interoperable legal frameworks that link EU instruments, national bilateral pacts and NATO planning. That includes templates for rapid consultations, common standards for transfers and legal clauses that specify triggers for stepped responses.

3) Tie reconstruction and economic integration to defence resilience. EU accession processes, regulatory alignment and reconstruction funding can increase Ukraine’s systemic resistance to coercion, but they must be paired with the hard capabilities that underpin any guarantee.

Conclusion

The security guarantees Ukraine needs will be as much about capabilities and institutions as they are about words on paper. The bilateral pacts concluded in early 2024 demonstrate a pragmatic pathway toward sustained Western backing, but they do not yet replace the legal shelter of NATO. For the EU, the strategic choice is whether to remain primarily an economic and political anchor for Kyiv or to invest in the defence instruments that can turn promises into deterrence. The coming years will test whether Europe can convert bilateral goodwill into an integrated security architecture that is credible, enduring and acceptable to both Kyiv and the wider alliance community.