Ukrainian NATO Membership

The North Atlantic Treaty Organization (NATO) binds the United States, Canada, and thirty European countries to the idea of collective defense. That means an attack on one member would be treated as an attack on all. During the Cold War, that promise of a collective response to aggression helped deter conflict between NATO members and the Soviet Union. Now, Russia’s aggression toward its neighbors poses a new test for the alliance. Ukraine formally applied for NATO membership in 2022, months after Russia invaded the country. Extending the guarantee of collective defense to Ukraine could deter Russia from launching another invasion in the future. However, if deterrence failed, Ukrainian NATO membership could draw the alliance directly into a war with Russia. Such a war could have dangerous consequences, including nuclear escalation.

Ukraine’s desire for NATO membership is decades in the making. Following its independence from the Soviet Union in 1991, the country tried to maintain a delicate balance between managing its relationship with Russia and building closer ties with the United States and Western Europe. Russia maintains that Ukraine should be part of its sphere of influence. Accordingly, it has regarded Ukrainian integration into Western institutions such as NATO and the European Union (EU) as a threat.

Tensions came to a head in 2014 when Ukraine moved toward signing an agreement to deepen trade relations and political cooperation between Ukraine and the EU. Fearing Ukraine was slipping out of its orbit, Russia invaded and annexed the Ukrainian territory of Crimea. It then began supporting separatist movements in eastern Ukraine. Undeterred, Ukraine went forward with the EU agreement and made membership in both the EU and NATO a formal goal. Meanwhile, Russia remained vehemently opposed to the idea of Ukrainian membership in those organizations—NATO in particular—characterizing it as an attempt by hostile powers to encircle Russia.

Russia’s 2022 invasion made the question of Ukrainian NATO membership even more urgent. With substantial Western military and financial support, Ukraine has resisted Russia's invasion and regained significant amounts of the territory that Russia initially occupied. As the fighting continues, Ukrainian President Volodymyr Zelenskyy has repeatedly called for quick entry into NATO. Only membership in the alliance, he argues, can guarantee Ukraine’s sovereignty and deter further Russian aggression.  

Some NATO countries—particularly those nearest Russia in eastern Europe and the Baltic region—support Ukraine’s bid. They argue that inviting Ukraine to join NATO would offer the strongest message to Russia that its invasion of Ukraine was counterproductive. It would also signal that further aggression, against Ukraine or any NATO member, would mean war with NATO. Some members also claim that admitting Ukraine would strengthen NATO. Even with the casualties it has sustained, Ukraine has Europe’s largest army after Russia. Furthermore, its forces are now battle-hardened and better equipped to cooperate with NATO militaries because of Western military support.

However, other NATO members—including the United States—urge caution. They stress that admitting Ukraine into NATO cannot guarantee an end to Russian aggression. If deterrence failed, they point out that NATO members could be forced to choose between joining a future war with Russia or discrediting NATO’s core principle of collective defense. Critics also argue that the prospect of NATO membership for Ukraine in the future is an impediment to peace now. Russian President Vladimir Putin has insisted that taking Ukrainian NATO membership off the table is a nonnegotiable condition for any peace deal. Inviting Ukraine to join could prompt him to simply prolong the conflict.

Some policymakers have proposed alternative arrangements for Ukraine’s future security. Those include offering assurances from individual NATO members that they will continue to provide Ukraine the support it needs to defend itself. Some European countries also envisage a coalition of countries that would deploy forces to Ukraine after the end of the conflict to help deter future aggression. Ukraine is also a candidate for membership in the EU, which would provide Ukraine a formal security guarantee. Those proposals all fall short of providing Ukraine the security guarantee it wants from NATO. Still, they represent viable alternatives for providing Ukraine concrete support.  

Ultimately, the debate over Ukrainian NATO membership will remain a defining question in the war and any peace process that follows. No matter how the alliance chooses to answer that question, it will have enormous implications for peace and stability in Europe.