NATO's 2 closest partners are doing some hard thinking about the alliance after Russia's attack on Ukraine

• Russia's invasion of Ukraine has prompted new interest in NATO membership in Sweden and Finland.
• The two countries have strategically valuable locations in Northern Europe and already work closely with NATO.

Russia's invasion of Ukraine has Finland and Sweden concerned. The two Nordic countries have strategically valuable locations next to their larger neighbor: Finland has an 830-mile border with Russia, and Sweden overlooks important maritime routes through the Baltic Sea.

While Russia has threatened neither country directly since its February 24 invasion, Moscow's aggression has reignited debate in those countries about their security — including whether they should finally seek NATO membership.

Before joining the EU in 1995, Sweden and Finland were politically neutral. They remain militarily non-aligned, but they are two of NATO's Enhanced Opportunities Partners, the closest form of cooperation offered to non-members. They have participated in NATO's Response Force and frequently conduct joint exercises with the alliance.

After Russia's invasion, the two countries entered into enhanced intelligence-sharing cooperation with NATO, and their foreign ministers attended NATO's emergency summit on March 4 — moves that highlighted the importance of their relationship with the alliance.

A fragile balance

Historically, both countries have been against NATO membership. Yet following the Russian invasion of Ukraine, 53% of Finns expressed support for joining, up from 19% in 2017. Similarly, a record-setting 51% of Swedes supported NATO membership in a poll this month.

"Both Finland and Sweden are clearly moving toward NATO membership," Leah Scheunemann, deputy director of the Atlantic Council's Transatlantic Security Initiative, told Insider.

Finland's president said this month that the country would review the "alternatives and risks" related to membership, and Finland's prime minister, who previously ruled out pursuing membership, has said discussions on joining should take place with the goal of building a national consensus.

Finland is "more likely to join NATO sooner than Sweden" but probably not until after the April 2023 parliamentary elections, "given parliamentary discussions already underway [and] the current situation in Ukraine," Scheunemann said.

In Sweden, the opposition in parliament has called for a debate over NATO membership, but Swedish Prime Minister Magdalena Andersson has said applying to join would "further destabilize this area of Europe and increase tensions."

Russia has warned both Finland and Sweden against joining NATO. Days after Russia's invasion, Russian Foreign Ministry spokeswoman Maria Zakharova said Russia would retaliate should either country seek membership.

If Finland and Sweden do join NATO, Russia will likely be frustrated "but unable to do anything due to how thinly it has stretched itself in its invasion of Ukraine," Jason Moyer, an associate at Wilson Center's Global Europe Program, told Insider.

"I find it difficult to imagine Russia opening up an additional front by attacking another country, given reports of poor morale, inadequate supplies, and slow progress of Russian forces in Ukraine," Moyer added.

But Russia is a major trade partner of both countries and could exert significant economic pressure, Moyer said. "Finland in particular is very dependent on Russian energy resources with about two-thirds of its oil and gas imports [coming] from Russia."

Hedging their bets

Sweden and Finland are taking multiple approaches to guarantee their security.

Both are members of Nordic Defence Cooperation, a regional security grouping with NATO members Iceland, Denmark, and Norway. Both have also enhanced their security cooperation with each other, with the EU, and through security arrangements with the UK, Denmark, and the Baltic States, Scheunemann said.

Sweden and Finland have also increased their cooperation with the US "in really historic ways," Scheunemann added.

On March 5, Finnish President Sauli Niinisto met President Joe Biden in Washington, where they committed to strengthen US-Finnish security cooperation. During their meeting, they also spoke with the Swedish prime minister, highlighting the very close relationship between Finland and Sweden.

There remain some limits on their cooperation with the US, however. Neither country has been designated a major non-NATO ally by the US, which would bring financial and security benefits.

Ahead of the EU summit held last week in response to events in Ukraine, the Swedish and Finnish prime ministers reminded their EU partners of the bloc's "obligation" to aid a member facing armed aggression, a commitment enshrined in the EU's foundation treaty.

EU members would honor that obligation were Finland or Sweden attacked, Moyer said. "However, as a deterrent, the EU pales in comparison to the security guarantee offered by NATO membership, the gold standard in defensive alliances."

In addition to bilateral and multilateral cooperation, the two countries are each increasing their own defense investments.

In December, Finland announced that it would buy 64 F-35A fighters jets in its largest defense purchase ever. It will also expedite its purchase of additional ground-launched anti-aircraft missiles.

On March 10, Sweden announced plans to spend 2% of GDP on defense in the years ahead, again raising defense expenditure since it fell to a low of 1.02% of GDP in 2017.

Fast-track accession

NATO accession requires all members to approve and ratify the decision and can be a years-long process.

Nevertheless, NATO Secretary General Jens Stoltenberg recently said that it should be possible for Sweden and Finland to join "rather quickly" given their "high level of interoperability" with NATO.

The process could take "only a few months," and NATO members could extend provisional security guarantees to them during ratification, which could be the longest phase, Scheunemann told Insider.

Amid the turmoil in Europe, the two Nordic countries face a decision with significant geopolitical implications.

"We have safe solutions also for our future," Niinistro said this month. "We must review them carefully. Not with delay, but carefully."

Constantine Atlamazoglou works on transatlantic and European security. He holds a master's degree in security studies and European affairs from the Fletcher School of Law and Diplomacy. You can contact him on LinkedIn.