Will Finland and Sweden Join NATO?

One consequence of Russia’s invasion of Ukraine may be the exact thing Russian president Vladimir Putin, the war’s architect, has indicated he did not want: the enlargement of NATO, starting with Finland and Sweden.

Public polling in Finland and Sweden has shown a clear swing in favor of joining NATO since the war in Ukraine began. This week, Finland submitted a report on security to its parliament, the centerpiece of which is a discussion about joining NATO. Finnish prime minister Sanna Marin met with her Swedish counterpart Magdalena Andersson to discuss the report and consider “how to strengthen the security of Finland and Sweden in the changed security environment.” Marin said Finland will decide whether to apply to join NATO “within weeks.” In response, former Russian president Dmitry Medvedev has warned that “there can be no more talk of any nuclear–free status for the Baltic,” alluding to the potential deployment of Russian nuclear capabilities in the region if Finland and Sweden were to join the alliance.

In light of these events, what are the prospects for Finland and Sweden joining NATO, what is the process, and what are the likely consequences?

Q1: Why are Finland and Sweden not already members of NATO?

A1: Finland and Sweden both have a long history of nonalignment and neutrality on security and defense. Although their histories with Russia are not without their violent moments, and the foreign policy strategies and statements of both have been clear-eyed about the Russian threat, Finland and Sweden have opted to remain militarily non-aligned and outside of NATO.

Both nations have preferred to pursue a balanced security policy toward Russia. On the one hand, they frequently cooperate on defense matters with the United States, NATO, and friendly northern European nations via “minilateral” arrangements such as the Nordic Defence Cooperation or UK-led Joint Expeditionary Force. On the other, and even after Russia’s initial aggression in Ukraine in 2014, both have sought to maintain a robust dialogue with Moscow and avoid provoking their powerful eastern neighbor—a particular concern for Finland, which shares an 832-mile (1,300-kilometer) land border with Russia (Sweden shares no border with Russia, although it does own the strategically important island of Gotland in the Baltic Sea).

This balanced approach has not prevented Finland and Sweden from developing a close relationship with NATO in recent decades. Both countries joined NATO’s partnership for peace program in 1994 and have contributed to NATO-led operations and missions in the Balkans, Afghanistan, and Iraq. Following Russia’s invasion of Ukraine, NATO has accelerated its cooperation with Helsinki and Stockholm in terms of intelligence sharing and political coordination. Both countries have been invited to NATO’s foreign and defense ministerial meetings as well as the extraordinary summit on March 24. Finnish and Swedish armed forces have also participated in recent NATO exercises on the eastern flank.

Q2: What has changed in Finland and Sweden to put NATO membership on the agenda?

A2: In Finland, the tide has changed in response to Russia’s invasion. Recent public opinion polls have shown a clear shift: a March poll indicated that up to 62 percent of Finnish citizens are now in favor of joining the alliance, with only 16 percent opposing the move. This is a significant change from the 21 percent in favor in a 2017 poll. A recent survey found almost identical sentiment among Finnish parliamentarians. Major parties who traditionally opposed NATO membership—the Center Party and Social Democrats—are reevaluating their stance. Overall, reporting indicates that only the small Left Alliance party remains formally opposed.

The Finnish government’s report—Government report on changes in the security environment—presented its view that the security environment has clearly changed as a result of Russia’s invasion of Ukraine. As a result, it assesses the parameters of Finnish NATO membership. While the document stops short of proposing an immediate application, the section on NATO membership repeatedly underlines that Finland would be made safer under NATO’s collective defense umbrella and preemptively addresses the likely concerns of the Finnish people regarding, for example, whether NATO membership would oblige Finland to accept nuclear weapons—which it does not.

As for the domestic decisionmaking process, the report also notes that it is not entirely settled. It is likely that the Finnish Parliament’s Constitutional Law Committee would need to decide whether a majority vote is sufficient to apply for NATO membership or whether a two-thirds vote is required. The Finnish Parliament will begin to debate the matter next week and Prime Minister Sanna Marin has said she believes the body will make decisions in weeks, not months.

The Swedish people have historically viewed the prospect of NATO membership more favorably than the Finnish public. Polls over the past decade show consistent support ranging between 31 and 37 percent in favor. A post-invasion poll shows that number may now be 59 percent. The center-right opposition parties support membership, and the far-right Sweden Democrats seem to be rethinking their anti-NATO stance. However, the long-governing Social Democrats, who currently lead Sweden in a single-party minority government, have historically opposed NATO membership. The party is now conducting an “internal debate” on the matter. The government they lead is also reviewing its security policy, just like Finland. These two processes are expected to conclude in the next two months, and if they result in Social Democratic support for NATO membership, a formal application could follow as early as June. The Swedish general election in September is also critically timed and could tip the balance given the widespread public support for joining NATO.

Despite their differing situations, both countries have maintained that they would prefer to apply together. An early Finnish application would also put strong pressure on the Swedes to join—not least because Sweden may then become vulnerable to Russian attempts to intimidate them not to follow suit. An extended period of debate may also invite interference in the process or threats to either nation during the accession and transition process, during which NATO’s Article 5 mutual defense clause would not apply.

If Finland and Sweden decide whether to apply in the coming weeks, it will come just in time for NATO’s historic June summit in Madrid, where it will also agree on a new Strategic Concept to guide its activities in the decade ahead.

Q3: What is the process for joining NATO?

A3: It is up to individual nations whether and when to apply for membership in NATO. The alliance’s so-called open-door policy was established under Article 10 of the Washington Treaty, its founding document. In its own words, “NATO’s door remains open to any European country in a position to undertake the commitments and obligations of membership, and contribute to security in the Euro-Atlantic area.” Accession requires a consensus of existing NATO members who may, “by unanimous agreement, invite any other European State in a position to further the principles of this Treaty and to contribute to the security of the North Atlantic area to accede to this Treaty.”

The accession process requires several steps. Once a national decision is made, aspirant countries inform NATO of their intent. After a period of consultation, NATO members send back an invitation to apply, triggering accession negotiations. Then the aspirant must demonstrate they meet the criteria for NATO membership, which include political, military, and economic goals. Examples of these include resilient democratic institutions, a commitment to the peaceful resolution of conflicts, and sufficient investment in modern and capable military forces. The purpose of the membership criteria is to make sure aspirants are, in accordance with Article 10, “in a position to further the principles of this Treaty and to contribute to the security of the North Atlantic area.” Applicants not meeting the criteria are offered support through a Membership Action Plan, a process that Bosnia and Herzegovina is now going through. Other nations which have declared their aspirations to NATO membership include Georgia and Ukraine.

After negotiations conclude, an Accession Protocol document is sent to the national legislatures of all NATO allies, who ratify it according to their own domestic procedures. After a few more bureaucratic formalities, the aspirant country is officially invited to join the alliance.

Importantly, there is no set timeline for this process. It is simply a matter of the extent to which the aspirant country already meets NATO’s criteria and the political will of NATO allies to let them in. Neither is in dispute for Finland or Sweden. As NATO secretary general Jens Stoltenberg has said, “We know that they can easily join this alliance if they decide to apply.” The process within NATO could therefore happen quickly and even be accelerated.

Any delay would likely be down to the time taken by domestic ratification among NATO’s 30 existing members. For example, the ratification process for NATO’s latest member, North Macedonia, lasted 13 months. This is not to rule out the minor threat of “spoilers” within the alliance who could slow-walk the process or refuse to ratify the Accession Protocol in the pursuit of extracting concessions on some other policy goal. Although Hungary has deployed this tactic in other circumstances, including those involving Ukraine’s accession to NATO, there has been no indication they would in this instance.

Q4: What do Finland and Sweden bring to the alliance?

A4: Finland and Sweden possess highly advanced militaries and civil defense capacities that would bring substantial capability and expertise to NATO—and add to the total forces the alliance can bring to bear in a collective defense or crisis management scenario.

Both nations are widely considered to be leading security providers in Europe. They are already NATO Enhanced Opportunity Partners, which allows for closer consultations and joint military exercising. Operationally speaking, this means Sweden and Finland are already well integrated into NATO and have a considerable degree of military interoperability with allied nations. Finnish and Swedish forces could easily fight under a NATO flag with little operational friction very soon after joining.

Finland and Sweden both boast high-quality, professional militaries with advanced capabilities at sea, on land, and in the air—for example, Finland is procuring 64 F-35s. Both have discussed increasing their defense budget in the coming years, including to reach the NATO target of spending at least 2 percent of GDP on defense. Finland appears to have already accounted for this in its report, predicting an increase in its defense budget of up to 1.5 percent.

The addition of new members is also a matter of geography. Although NATO is a defensive alliance, Russia will inevitably be drawn to devote greater resources to its border with Finland and the Baltic Sea—a vital area for European shipping, to which both countries will add significant naval defense forces. Similarly, as NATO increasingly considers a role for itself in the “High North,” the Arctic-specific capabilities, expertise, and skills of both countries will also add value.

Finally, both nations have much to share with allies given their long-standing efforts to build societal resilience against Russian disinformation, emphasizing civic preparedness and national self-defense. Finland’s approach of “Comprehensive Security” and Sweden’s “Total Defense” concept are widely seen as models of best practice across Europe. Finland also hosts the European Centre of Excellence for Countering Hybrid Threats, which has 31 members from across NATO and the European Union.

Q5: How might Russia respond if Finland and Sweden apply?

A5: The greatest concern following a Finnish or Swedish application is not whether NATO will accept them; it is what Russia might do in the period after application but before they join and are formally protected by NATO’s collective defense guarantee. Russia has already begun to threaten Finland rhetorically, violate Finnish airspace, and conduct cyberattacks against government websites. The question is whether these attempts at “hybrid influencing” measures—as the Finnish report calls it—may presage conventional aggression.

This depends on Russia’s intent to attack and its capability to do so, particularly given the extensive damage to Russia’s economy (through sanctions) and military in Ukraine. Regarding intent, it is likely Putin has long since recognized that Sweden and Finland are intimately aligned with NATO, with or without formal membership. An invasion would therefore achieve little beyond heavier sanctions, further isolation, and military losses. And yet this did not stop Russia from invading Ukraine.

Regarding capability, it remains to be seen whether Russia’s heavy military losses in Ukraine so far will increase in a drawn-out conflict focused on east and south Ukraine. The loss of the Russian warship Moskva, its flagship Black Sea missile cruiser, indicates the likelihood of significant further losses. That said, Russia’s conventional forces remain significant and highly capable, including its land and air forces in the Western Military District, its Baltic Fleet and missile forces in Kaliningrad and the Gulf of Finland, and the Northern Fleet based on the Kola Peninsula.

To deal with any potential threat, NATO has already indicated it would provide security guarantees for the interim period, and discussions are underway in Brussels to determine what form these would take. Other military formations focused on Northern Europe may also have a role to play here, such as the Joint Expeditionary Force. Furthermore, as members of the European Union, Finland and Sweden are also theoretically covered by the European Union’s mutual assistance clause enshrined in Article 42(7) of the Treaty on European Union.

If Finland and Sweden apply to join NATO, it will be up to the leaders and domestic populations of the alliance’s 30 existing members to decide whether the value of Finnish and Swedish membership is worth the risk of being drawn into a conflict on their behalf. Thanks to Russia’s invasion and war of aggression in Ukraine, it seems likely they will be asked to consider this question sooner rather than later, probably at NATO’s Summit in Madrid at the end of June.

Colin Wall is a research associate with the Europe, Russia, and Eurasia Program at the Center for Strategic and International Studies in Washington, D.C. Sean Monaghan is a visiting fellow with the Europe, Russia, and Eurasia Program at CSIS. Pierre Morcos is a visiting fellow with the Europe, Russia, and Eurasia Program at CSIS.

Critical Questions is produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s).

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Colin Wall

Colin Wall

Associate Fellow, Europe, Russia, and Eurasia Program
Sean Monaghan
Visiting Fellow, Europe, Russia and Eurasia Program

Pierre Morcos