Sweden has formally joined NATO as the 32nd member of the transatlantic military alliance, ending decades of post-World War II neutrality and centuries of broader non-alignment with major powers as security concerns in Europe spike following Russia's 2022 invasion of Ukraine. US President Joe Biden congratulated Sweden on its admission and said it was a sign that Russia's intervention in Ukraine had united, rather than divided, the alliance.
"When Putin launched his brutal war of aggression against the people of Ukraine, he thought he could weaken Europe and divide NATO," Biden said in a statement, which he is expected to echo in his State of the Union address to Congress today.
Swedish Prime Minister Ulf Kristersson with US Secretary of State Antony Blinken, holding Sweden's NATO Instruments of Accession in the Benjamin Franklin Room at the US State Department. (AP)"Instead, in May 2022, Sweden and Finland – two of our close partners, with two highly capable militaries – made the historic decision to apply for full NATO membership.
"With the addition of Sweden today, NATO stands more united, determined, and dynamic than ever – now 32 nations strong."
Swedish Prime Minister Ulf Kristersson and US Secretary of State Antony Blinken presided at a ceremony in which Sweden's "instrument of accession" to the alliance was officially deposited at the State Department.
"This is a historic moment for Sweden. It's historic for the alliance. It's historic for the transatlantic relationship," Blinken said.
US President Joe Biden, right, meets with Kristersson. (AP)"Our NATO alliance is now stronger, larger than it's ever been."
"Today is truly a historic day," Kristersson said.
"We are humbled, but we are also proud. We will live up to high expectations from all NATO allies. United we stand. Unity and solidarity will be Sweden's guiding light
Later Thursday, Kristersson was to visit the White House and then be a guest of honour at Biden's State of the Union address.
NATO Secretary-General Jens Stoltenberg also described it as "a historic day."
"Sweden will now take its rightful place at NATO's table, with an equal say in shaping NATO policies and decisions," he said in a statement.
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The Swedish flag will be raised outside the military organisation's headquarters in Brussels on Monday.
Stoltenberg underscored that the Nordic country "now enjoys the protection granted under Article 5, the ultimate guarantee of allies' freedom and security."
Article 5 of NATO's treaty obliges all members to come to the aid of an ally whose territory or security is under threat. It has only been activated once – by the US after the September 11, 2001, attacks – and is the collective security guarantee that Sweden has sought since Russia invaded Ukraine.
"Sweden's accession makes NATO stronger, Sweden safer and the whole alliance more secure," Stoltenberg said. He added that the move "demonstrates that NATO's door remains open and that every nation has the right to choose its own path."
The war in Ukraine enters its third year with little hope of immediate peace. (AP)Sweden, along with Finland, which joined NATO last year, both abandoned long-standing military neutrality that was a hallmark of the Nordic states' Cold War foreign policy after Russia invaded Ukraine in early 2022.
Biden, in his speech to US Congress, was expected to use Sweden's decision to join to step up calls for reluctant Republicans to approve stalled military assistance to Ukraine as the war enters its third year.
Biden and his NATO counterparts have vowed that Ukraine will join one day, too.
Sweden's membership had been held up due to objections by NATO members Turkey and Hungary. Turkey expressed concern that Sweden was harbouring and not taking enough action against Kurdish groups that it regards as terrorists, and Hungary's populist President Viktor Orban has shown pro-Russian sentiment and not shared the alliance's determination to support Ukraine.
After months of delay, Turkey ratified Sweden's admission earlier this year, and Hungary did so this week.