After two centuries of neutrality and two years of diplomacy, Sweden officially became the 32nd member of the North Atlantic Treaty Organization (NATO) on Thursday, the US government said.

Both the Swedish and US governments had indicated earlier in the day that the process would be finalized on Thursday during Prime Minister Ulf Kristersson's visit to Washington. 

"We will strive for unity, solidarity and burden-sharing, and will fully adhere to the Washington Treaty values: freedom, democracy, individual liberty and the rule of law. Stronger together," the Swedish prime minister's official account said in a post on X.

US President Joe Biden said he was "honored to welcome" Sweden as the alliance's newest member, adding that transatlantic security was stronger than ever.

A 'historic' day for NATO alliance

Sweden's NATO accession went into effect after 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 alliance. It's history for the transatlantic relationship," US Secretary of State Antony Blinken said at the accession ceremony.

NATO Secretary General Jens Stoltenberg wrote on X that "Sweden’s accession makes NATO stronger, Sweden safer, and the whole Alliance more secure." 

"Today is a truly historic day. Sweden is now a member of NATO," Kristersson said. "We will defend freedom together with the countries closest to us – both in terms of geography, culture and values," he added. 

The Swedish flag is expected to be hoisted at NATO headquarters in Brussels, Belgium, on Monday.

NATO expands in the shadow of Russia's invasion of Ukraine

Russian leader Vladimir Putin has justified his war in Ukraine by claiming that NATO had promised Russia it would not expand after the Cold War. Such an agreement was never made.

Blinken said that few would have expected Sweden and Finland to join the alliance before Putin ordered the invasion of Ukraine in February 2022. Finland joined NATO last year.

There is "no clearer example than today of the strategic debacle that Putin's invasion of Ukraine has become for Russia," Blinken said.

Ukrainian President Volodymyr Zelenskyy said Sweden was now "more protected from Russian evil." Ukraine applied to be a NATO member in 2022, but a timeline for its membership has yet to be determined.

Later in the evening, Biden will deliver the final State of the Union address of his term, with Kristersson joining First Lady Jill Biden in the assembly room.

Sweden ends two centuries of non-alignment

While already militarily intertwined with the US and members of the European Union, Sweden has not been involved in a war since the Napoleonic conflicts of the early 19th century, remaining neutral in both world wars in the 20th century.

However, in the wake of Russia's full-scale invasion of Ukraine in February 2022, Sweden joined Nordic neighbors Finland in applying for membership in NATO.

While Finland, which shares a 1,340-kilometer (830-mile) border with Russia, was welcomed into the alliance in April 2023, Sweden's candidacy stalled due to a diplomatic dispute with NATO member Turkey, which demanded that Stockholm clamp down on people in Sweden, often Kurds, deemed militants by Turkey.

Turkish President Recep Tayyip Erdogan later demanded action after protesters made use of liberal Swedish laws on freedom of expression to burn copies of the Koran.

Further obstacles were posed by Hungary whose nationalist prime minister Viktor Orban has boasted of his ties to Russian President Vladimir Putin and been a regular thorn in the side of western efforts to support Ukraine.

NATO exercise: Sweden already involved

NATO's Nordic Response Exercise is currently taking place in northern Sweden, Norway and Finland, involving 20,000 NATO troops from 13 countries, including Swedish marines.

Russian Security Council Secretary Nikolai Patrushev, a top ally of President Vladimir Putin, said on Thursday that the exercise looked like a rehearsal for an armed confrontation with Russia. According to the Interfax news agency, he called it "destabilizing" and said it was "raising tensions."

As a NATO member, Sweden, with its cutting-edge submarines and Gripen fighter jets, will be a crucial link between the Atlantic and the Baltic states.

A recent poll by Swedish broadcaster SR said that most Swedes believe the country made too many sacrifices to join NATO, although more than three-quarters believed NATO would boost the country's security.

Russia said it would adopt unspecified military-techniques and other countermeasures in response to Sweden joining the alliance.

rm, mf/msh (Reuters, dpa, AFP)