Sweden officially joined NATO today (March 7) and became the 32nd member of the transatlantic military alliance.

European security concerns have heightened after Russia invaded Ukraine in 2022, ending the country’s decades of post-World War II neutrality.

US President Joe Biden congratulated Sweden on joining and said it was a sign that Russian President Vladimir Putin’s intervention in Ukraine was uniting the alliance rather than dividing it.

He said: “When Putin launched a brutal war of aggression against the people of Ukraine, he thought he could weaken Europe and divide NATO.

“Instead, in May 2022, Sweden and Finland – two of our close partners with two powerful militaries – took the historic decision to apply for formal membership in NATO.

“With today’s addition of Sweden, NATO is more united, committed and energized than ever – now 32 countries strong.”

Swedish Prime Minister Ulf Kristersson and Secretary of State Antony Blinken presided over a ceremony for Sweden’s “Acts of Accession” to join the alliance, formally depositing it with the State Department.

“This is a historic moment for Sweden. This is historic for the alliance. This is historic for the transatlantic relationship,” Mr Blinken said, adding: “Our NATO alliance is now stronger than ever Stronger and bigger than ever.”

“Today is truly a historic day,” Christerson said. “We are humbled, but also proud. We will live up to the high expectations of all NATO allies. Unity is strength. Unity and solidarity will be Sweden’s guiding light.

Later today, Mr. Christerson will visit the White House before attending Biden’s State of the Union address as guest of honor.

NATO Secretary General Jens Stoltenberg also described it as a “historic day.”

“Sweden will now take its rightful place at the NATO negotiating table and have an equal voice in shaping NATO policy and decision-making,” he said in a statement.

The Swedish flag will be raised outside the military organization’s headquarters in Brussels on Monday. Stoltenberg stressed that the Nordic countries “now enjoy the protection conferred by Article 5, which is the ultimate guarantee of the freedom and security of the Allies.”

After Russia invades Ukraine in 2022, Nordic countries apply to join NATO

Article 5 of the NATO Treaty obliges all member states to provide assistance to allies whose territory or security is threatened.

It has only been activated once by the United States after the attacks of September 11, 2001.

“Sweden’s membership makes NATO stronger, Sweden more secure and the entire alliance more secure,” Stoltenberg said.

He added that the move “shows that NATO’s door remains open and that every country has the right to choose its own path.”

Sweden and Finland, which joined Nato last year, have both abandoned longstanding military neutrality that was a hallmark of the Nordic countries’ Cold War foreign policy in the wake of Russia’s invasion of Ukraine.

In his speech to Congress, Biden is expected to use Sweden’s decision to join to further appeal to reluctant Republicans to approve military aid to Ukraine as the war enters its third year.

Sweden’s membership was put on hold due to opposition from NATO members Turkey and Hungary.

Turkey has expressed concern that Sweden is harboring and not taking enough action against Kurdish groups it considers terrorists.

Hungary’s populist President Viktor Orban has shown pro-Russian sentiment but does not share the coalition’s determination to support Ukraine.

After months of delays, Turkey approved Sweden’s accession earlier this year, and Hungary did the same this week.

Additional reporting by Associated Press.