Why Finland and Sweden weren’t previously part of NATO

Reservists from Finland's Karelia Brigade train in southeastern Finland in March. (Lauri Heino/Lehtikuva/AP)

Western nations founded NATO in 1949 as a means of collective security against the Soviet Union and its allies. But for more than 70 years, two European countries — Finland and Sweden — declined to join the alliance, instead pursuing careful Cold War policies of neutrality and nonalignment.

But now, just three months after Russia invaded Ukraine, both Finland and Sweden have abandoned those policies and formally requested to join NATO. On Wednesday, the two countries delivered letters to NATO’s headquarters in Brussels to mark the official start of the accession process.

It’s a move that will transform Europe’s security landscape and expand Russia’s border with NATO. Finland and Sweden, both functioning democracies with well-trained armies, will also gain protection under the alliance’s Article 5 collective defense mechanism.

Here’s how the two nations got here.