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.

The documents are put into a vault at the State Department, which serves as the treaty depositary for NATO.

“With receipt of this instrument of accession let me be the very first to welcome Sweden as a party to the Washington Treaty and the 32nd member of the North Atlantic Treaty Organization,” Secretary of State Antony Blinken said alongside Kristersson.

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.

Sweden and its neighbor Finland – which shares a 1,300 kilometer (830 mile) border with Russia – both bid to join the bloc after Moscow launched its full-scale invasion of Ukraine.

Finland officially joined in April 2023, more than doubling NATO’s border with Russia in a blow to President Vladimir Putin who has sought to prevent any growth of the alliance.

But 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 Secretary General Jens Stoltenberg said Sweden’s accession “makes NATO stronger, Sweden safer and the whole alliance more secure. I look forward to raising their flag at NATO HQ on Monday.”