Sweden officially joined NATO on Thursday, March 7, a major shift from the country's decade old tradition of "neutralty"

Swedish Prime Minister, Ulf Kristersson formally handed over treaty 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 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 shares a 1,300 kilometer (830 mile) border with Russia.

“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 talked about 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.

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.

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