Finland has been welcomed as the newest member of the Nato defence alliance, with its admission marked on Tuesday, at a Nato meeting in Brussels.
The country joins in the wake of Russia's invasion of Ukraine, with Sweden also seeking to join the alliance.
The success of Finland's application hinged upon the approval of member state Turkey, which had previously obstructed the attempt to join the defence alliance for several months, accusing the Nordic country of "housing Kurdish terrorist organisations".
However, the parliament in Ankara voted unanimously to approve the application last week.
Speaking in Brussels, Nato Secretary General Jens Stoltenberg said it will give Finland "an ironclad security guarantee" and added, "this will make Finland safer and Nato stronger".
"On this very day, in 1949, the Washington Treaty – Nato's founding treaty – was signed in Washington and it’s hard to imagine a better way of celebrating our anniversary than to have Finland becoming a full member of the alliance," he said.
UK Prime Minister Rishi Sunak said: "This is an historic day for Finland and for Nato. Their accession has made our alliance stronger and every one of us safer.
"All Nato members now need to take the steps necessary to admit Sweden too, so we can stand together as one alliance to defend freedom in Europe and across the world."
Why does Finland matter?
From a military perspective, Russia's neighbour Finland would offer a large boost to Nato's northern European assets, not only bringing enhanced capabilities but an increased deterrence in the region, against a backdrop of the Russian invasion of Ukraine.
Finland's armed forces have already proven themselves highly compatible with Nato member states, frequently working with them on international missions and on exercises such as Exercise Arrow 22.
When asked about what Finland’s membership would mean for Russia's military attitude in the region, Mr Stoltenberg explained: "First of all, what we have seen over many years, is a Russian military build-up, also in the north, close to Finland, to Norway."
He added: "We have not only seen a Russian military build-up, but we've also seen that Russia, President Putin, is willing to use military force against neighbours – Georgia in 2008 then Crimea in 2014 and then the full-fledged invasion of Ukraine last year.
"This is part of a pattern and that is exactly why we have strengthened Nato, our readiness, our presence in the eastern part of the alliance and why our Nato allies are investing more in modern capabilities.
"It was actually the invasion of Ukraine last year that led to the decision by Finland and Sweden to apply for Nato membership."
Following claims Vladimir Putin wanted 'less Nato' on his Russian borders, Mr Stoltenberg said: "He's getting exactly the opposite. He's getting more troops, more readiness and more forces – land, sea and air – in the eastern part of the alliance.
"He's getting more members – Finland today and soon also Sweden.
"We are removing the room for miscalculation in Moscow about Nato's readiness to protect Finland".