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Swedish Prime Minister Ulf Kristersson hands accession documents to US Secretary of State Antony Blinken, March 7, 2024.
CNN  — 

Sweden officially joined NATO on Thursday after Russia’s invasion of Ukraine spurred it to rethink its defense policy and abandon its long held position of neutrality.

Swedish Prime Minister Ulf Kristersson formally handed over accession documents to the US State Department in Washington, DC, the final step of a months-long process to gain the approval of all members to allow his country to become the alliance’s 32nd member.

US Secretary of State Antony Blinken received the documents, which he said were the product of “nearly two years of tireless diplomacy” by NATO members. The documents are put into a vault at the State Department, which serves as the treaty depositary for NATO.

Sweden joining NATO was scarcely conceivable a little more than two years ago. The country remained neutral in both World Wars but when Russian troops began marching toward Kyiv in February 2022, Sweden – and its Nordic neighbor Finland – became alert to the threat Moscow could pose to nearby countries outside the alliance.

Finland – which shares a 1,300 kilometer (830 mile) border with Russia – officially joined in April 2023, more than doubling NATO’s border with Russia in a blow to President Vladimir Putin, who has sought to stem any growth of the alliance.

“If you step back and think of where we were three years ago, none of this was foreordained – and in fact, none of this was foreseeable,” Blinken said.

Blinken noted Sweden’s “200-year-old policy of non-alignment” – which stretches back to the Napoleonic Wars – and the Swedish population’s lack of appetite to join the alliance before Russia’s invasion.

“Then everything changed,” he said.

US President Joe Biden heralded Sweden’s accession, which he said made the bloc “more united, determined and dynamic than ever,” and able to “stand for freedom and democracy for generations to come.”

The move came just hours before Biden is set to deliver his State of the Union address, in which he is expected to draw sharp contrasts between his stance on issues of democracy and key alliances like NATO and that of his predecessor Donald Trump. Kristersson will be a guest of the First Lady at the address.

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UK Prime Minister Rishi Sunak also welcomed the news, describing it as a “historic moment.”

“Like Finland, Sweden shares our values and principles and they share our unwavering commitment to international security in the face of Russia’s threats and their barbaric war in Ukraine,” Sunak said. “Sweden and Finland’s membership will make NATO stronger and the whole Euro-Atlantic more secure.”

Ukrainian President Volodymyr Zelensky said Sweden’s accession was a win for everyone, calling the country “a strong ally and a country that can be trusted.”

“Ukraine has always supported Sweden in its pursuit of NATO membership, and I thank Sweden for its support of our country – there will be a day when Sweden will be able to congratulate Ukraine on joining the alliance as well. Together, we are always stronger,” he said.

Kristersson thanked his allies for welcoming Sweden into the bloc.

“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,” he said in a statement.

While Finland became NATO’s 31st member without major obstacles, Sweden’s bid to join the bloc was for months obstructed by Turkey and Hungary, which enjoy friendly relations with Moscow and delayed ratifying Stockholm’s accession.

Turkey’s parliament voted in January to approve Sweden’s bid after months of tensions between the two nations, sparked primarily by a spate of Quran-burning protests in Sweden that enraged Turkish lawmakers.

But Hungary made Sweden wait even longer, with Prime Minister Viktor Orban declining to green-light its bid on several occasions. Hungary’s parliament eventually approved Sweden’s accession last month.

NATO’s next annual summit will be held in July in Washington, DC, and will mark the alliance’s 75th anniversary.

CNN’s Betsy Klein contributed reporting.