Finland on Tuesday became an official member of the military alliance NATO, prompted by Russian President Vladimir Putin’s decision to invade Ukraine last year.

The Nordic nation is the 31st country to join the alliance, which vows in its treaty that an attack on one of its members is an attack on them all. It’s a historic moment for Finland, which has followed a path of neutrality for decades.

“Finland’s membership is not targeted against anyone. Nor does it change the foundations or objectives of Finland’s foreign and security policy,” Finnish President Sauli Niinisto said in a written statement Tuesday.

His comments came shortly after the country’s foreign affairs minister, Pekka Haavisto, handed over all the accession documents in Brussels, at NATO’s headquarters, in the presence of the group’s secretary general, Jens Stoltenberg, and U.S. State Secretary Antony Blinken.

“Welcome to the alliance,” Stoltenberg told Finnish representatives at the ceremony.