NATO's Nordic Expansion: How Russia's War Drove Finland and Sweden Into the Alliance

On 4 April 2023, Finland became NATO's 31st member. Less than a year later, on 7 March 2024, Sweden followed as the 32nd. The accession of these two Nordic countries represents the most significant expansion of NATO since the post-Cold War wave of Eastern European states joined in the 1990s and 2000s. It is also a strategic humiliation for Vladimir Putin. Russia's invasion of Ukraine was justified, in part, by the claim that NATO expansion threatened Russian security and had to be stopped. The result has been the exact opposite: NATO has expanded to Russia's doorstep, doubling the length of the alliance's border with Russia and transforming the Baltic Sea into a NATO lake. Finland and Sweden's membership is a case study in how aggression can backfire, how security assumptions can collapse overnight, and how a military alliance written off as obsolete has found new purpose in the face of renewed threats.

The historical context: neutrality as strategy

Finland's relationship with Russia is defined by geography and history. The two countries share a 1,300-kilometre border, the longest between Russia and any EU state. Finland was part of the Russian Empire until 1917 and fought two brutal wars against the Soviet Union in 1939-44, losing territory but maintaining independence. Throughout the Cold War, Finland practised a policy known as "Finlandisation"—maintaining neutrality and good relations with the Soviet Union to avoid provoking its vastly more powerful neighbour. This was not appeasement but pragmatism: Finland built a capable military, maintained conscription, and prepared to defend itself, but it did not join NATO or allow its territory to be used against the USSR.

Sweden's neutrality has deeper roots, dating back over two centuries. Sweden has not fought a war since 1814 and built its identity around non-alignment, staying out of both World Wars and the Cold War. Like Finland, Sweden maintained a strong military during the Cold War, but it framed this as defensive and independent, not aligned with either NATO or the Warsaw Pact. After the Cold War, both countries reduced their militaries and deepened cooperation with NATO through partnerships, but they stopped short of membership.

This changed on 24 February 2022. Russia's invasion of Ukraine was a shock that reverberated across Europe, but nowhere more so than in Finland and Sweden. If Russia would invade Ukraine—a country with which it has deep historical, cultural, and economic ties—then no neutral country could assume it was safe. The invasion demonstrated that Russian assurances of sovereignty were worthless, that neutrality was no guarantee of security, and that the only reliable deterrent was collective defence. Within weeks, public opinion in both countries shifted from majority opposition to NATO membership to majority support. By May 2022, both governments had formally applied to join.

The accession process: swift but not without obstacles

NATO's door is theoretically open to any European democracy that meets the alliance's standards and is accepted by all existing members. In practice, accession usually takes years of reforms, negotiations, and political wrangling. Finland and Sweden's process was remarkably swift—less than a year for Finland, less than two for Sweden—but it was not without obstacles.

The main hurdle was Turkey. President Recep Tayyip Erdoğan demanded that Sweden, in particular, take action against Kurdish groups that Turkey designates as terrorists and that have found refuge in Sweden. Erdoğan accused Sweden of harbouring members of the PKK (Kurdistan Workers' Party) and supporting groups linked to the 2016 coup attempt in Turkey. He blocked Sweden's accession for months, using it as leverage to extract concessions. Sweden eventually agreed to tighten its anti-terrorism laws, extradite some individuals, and lift an arms embargo on Turkey. Finland, which had fewer issues with Turkey, was allowed to proceed first.

Hungary also delayed Sweden's accession, with Prime Minister Viktor Orbán citing grievances over Swedish criticism of Hungary's democratic backsliding. The delay was widely seen as performative—Orbán eventually approved Sweden's membership in early 2024 after extracting symbolic concessions and attention.

The delays were frustrating but ultimately irrelevant. By mid-2024, both countries were full NATO members, and the alliance's northern flank had been transformed.

The military implications: a stronger NATO, a weaker Russia

Finland and Sweden are not small, weak countries seeking protection. They are capable military powers that make NATO significantly stronger.

Finland's military is one of the most formidable in Europe relative to the country's size. It maintains a peacetime force of around 23,000 active personnel, but through universal conscription and a large reserve system, it can mobilise 280,000 troops in wartime—more than the UK or France. Finland has invested heavily in artillery, air defences, and anti-tank weapons, and its military doctrine is built around defending against a Russian invasion. Finnish forces train in Arctic and forest environments that are among the most challenging in the world, and they have interoperability with NATO from years of exercises and partnerships.

Finland's geography is also strategically significant. Its 1,300km border with Russia is now NATO's border, and Finnish territory provides NATO with depth and options in the event of a conflict. The Finnish military has pre-positioned supplies, fortified key routes, and planned for decades to slow and bleed a Russian advance. Russia's Northern Fleet, based in Murmansk, is now flanked by NATO territory, and any Russian military activity in the Arctic or Baltic is under closer scrutiny.

Sweden brings different but equally valuable capabilities. Its defence industry produces some of the world's most advanced military equipment, including the Gripen fighter jet, the Archer artillery system, and the Gotland-class submarines, which are among the quietest in the world and ideally suited to the shallow waters of the Baltic. Sweden has a professional, well-trained military and a strong tradition of innovation in defence technology. Its accession gives NATO access to Swedish bases, airspace, and intelligence, and it completes NATO's control of the Baltic Sea.

Together, Finland and Sweden close a gap in NATO's northern defences. During the Cold War, the Baltic Sea was contested; now it is effectively a NATO lake, with all littoral states except Russia being NATO members or partners. This has profound implications for Russia's ability to project power in the region and for NATO's ability to defend the Baltic states (Estonia, Latvia, Lithuania), which are NATO members but were previously vulnerable to being cut off in a conflict.

Russia's response: bluster without bite

Russia's reaction to Finland and Sweden's NATO membership has been a mix of threats and impotence. Before the accession, Russian officials warned of "serious military-political consequences" and threatened to deploy nuclear weapons and additional forces near the Finnish border. Putin himself said that NATO expansion was a threat to Russian security and that Russia would respond.

In practice, Russia has done little. It has conducted military exercises near the Finnish border and moved some forces to the region, but it has also withdrawn forces from the area to reinforce the war in Ukraine. Russia has suspended military cooperation agreements with Finland and cut off gas supplies, but these are symbolic gestures with limited impact. Russia has not, and likely cannot, prevent Finland and Sweden from joining NATO, and the failure to do so is a strategic defeat.

The expansion of NATO to Russia's border undermines Putin's narrative that the war in Ukraine is about preventing NATO encroachment. NATO has now encroached far more than it would have if Russia had not invaded Ukraine. Finland and Sweden were content with non-alignment until Russia made it clear that neutrality was no protection. Putin's war has achieved the opposite of its stated aims: NATO is larger, more united, and more focused on Russia as a threat than at any time since the Cold War.

The broader implications: a new European security order

Finland and Sweden's accession is part of a broader shift in European security. The post-Cold War assumption that major war in Europe was obsolete has been shattered. Countries that reduced their militaries and relied on diplomacy and economic interdependence are now rearming and rethinking their security strategies. Germany has announced a €100 billion increase in defence spending. Poland is building one of the largest armies in Europe. The Baltic states are fortifying their borders and calling for permanent NATO bases.

NATO itself has been revitalised. The alliance was widely seen as adrift in the 2010s, with questions about its purpose and unity. Trump's presidency raised doubts about US commitment, and members disagreed over burden-sharing and priorities. Russia's invasion of Ukraine gave NATO a clear mission: deterring and, if necessary, defending against Russian aggression. Finland and Sweden's membership is both a symptom and a cause of this revitalisation—they joined because NATO is relevant again, and their membership makes NATO more capable.

For the UK, Finland and Sweden's accession strengthens an alliance that is central to British security. The UK has been a strong supporter of both countries' membership and has provided security assurances during the accession process. British forces have increased their presence in the Nordic and Baltic regions, and the UK has deepened defence cooperation with both countries. The UK's Joint Expeditionary Force, a coalition of northern European countries, now includes two NATO members in Finland and Sweden, enhancing its coherence and capability.

What comes next: consolidation and deterrence

The immediate task for NATO is to integrate Finland and Sweden fully into the alliance's command structures, defence plans, and exercises. This is already well underway—both countries have been NATO partners for years and are highly interoperable. The bigger challenge is political: ensuring that the alliance remains united and that all members contribute to collective defence.

The expansion also raises questions about NATO's future. If Finland and Sweden can join, what about Ukraine, Georgia, or Moldova? NATO has said its door remains open, but the reality is that admitting countries in active conflict with Russia (Ukraine) or with unresolved territorial disputes (Georgia, Moldova) would risk dragging NATO into war. The alliance is unlikely to expand further eastward in the near term, but the question will not go away.

For Russia, the expansion is a fait accompli. It cannot reverse Finland and Sweden's membership, and any attempt to intimidate or coerce them would only strengthen NATO's resolve. Russia's best option is to accept the new reality and focus on managing its relationship with NATO to avoid escalation. Whether Putin is willing or able to do so is another question.

Finland and Sweden's accession to NATO is a historic shift, the product of Russian aggression and the collapse of assumptions that shaped European security for decades. It is also a reminder that alliances matter, that geography and history shape strategy, and that actions have consequences. Putin wanted to stop NATO expansion; instead, he accelerated it. NATO was written off as obsolete; instead, it has found new purpose. And two countries that prized neutrality for generations have chosen collective defence, not because they wanted to, but because Russia left them no choice.