Assuming he does, Hungary would be the last remaining holdout. Officials there have previously signaled that they would not, ultimately, stand in the way. On Tuesday, Prime Minister Viktor Orban announced, somewhat cryptically, that he had invited the Swedish prime minister to visit to “negotiate on Sweden’s NATO accession.”

Swedish Prime Minister Ulf Kristersson appeared to respond only to the Turkish vote, writing on X, formerly Twitter, “Today we are one step closer to becoming a full member of NATO. Positive that the Grand General Assembly of Türkiye has voted in favour of Sweden’s NATO accession.”

If both Turkey and Hungary get on board, the alliance could formally welcome its 32nd member, potentially sealing the deal before its 75th anniversary this spring.

Four maps explain how Sweden and Finland could alter NATO’s security

Sweden joining NATO would mark a historic shift for a country that long maintained a policy of military nonalignment. It would bolster NATO’s air and sea capabilities, improving the alliance’s position in the Baltic Sea and the Arctic.

In thanking the Turkish parliament for its vote, the U.S. ambassador to Turkey, Jeff Flake, wrote, “Sweden’s accession to NATO is a critical step in strengthening the Alliance, which is today more important than ever.”

It would also eliminate one source of Western disunity of the sort relished by Russian President Vladimir Putin.

After Putin sent tanks into Ukraine and shook Europeans’ sense of their security, the ruling parties in Sweden and neighboring Finland endorsed becoming part of NATO, concluding they would be safer inside the alliance, even if their joining further angered Russia.

Ruling parties in Sweden, Finland back NATO membership in historic shifts

The two Nordic nations submitted coordinated bids. But each of NATO’s 30 member countries had to approve, and Turkey’s Erdogan quickly emerged as the main obstacle, using the process to secure concessions and score domestic political points.

Even after allowing Finland to join, Erdogan continued to object to Sweden, demanding that the country do more to crack down on groups Turkey regards as terrorist entities, including the Kurdistan Workers’ Party (PKK) and a movement accused of trying to overthrow the Turkish government in 2016. Erdogan got Stockholm to agree to continue counterterrorism cooperation, as well as lift an arms embargo on Turkey.

But analysts assessed that Turkey’s main goal was to secure a deal to buy F-16 fighter jets from the United States, as well as upgrades for its current fleet. In July, after Erdogan publicly dropped his opposition to Sweden’s NATO membership, the Biden administration said it intended to move ahead with the transfer of F-16s to Turkey.

The deal has faced resistance from senior members of Congress — though one of the staunchest opponents, Sen. Bob Menendez (D-N.J.), is no longer chairman of the powerful Senate Foreign Relations Committee. His replacement, Sen. Ben Cardin (D-Md.), has not expressed a position on the sale. While some senior lawmakers have said the Sweden vote would clear the way for the F-16s, others have insisted that there are broader problems with Turkey, including human rights violations and ongoing Turkish attacks on Kurdish U.S. allies in Syria.

“For much of the time President Erdogan has been in office, Turkey has been an unfaithful NATO ally — so this is welcome news,” said Sen. Chris Van Hollen (D-Md.). “That said, I still have questions about Erdogan’s ongoing attacks against our Syrian Kurdish allies, his aggressive actions in the Eastern Mediterranean and the role he played in supporting Azerbaijan’s military assaults against Nagorno-Karabakh. We need more answers and assurances about these concerns from both Turkey and the Biden administration before Congress moves forward with the sale of F-16s.”

President Biden held a call with Erdogan on Dec. 14, discussing Sweden’s bid and “further enhancing Türkiye’s NATO interoperability,” among other topics, according to a White House summary.

Secretary of State Antony Blinken also discussed Sweden’s NATO membership in a meeting with Erdogan this month.

To move forward on the F-16s, the administration would need to submit formal notification to Congress, after which lawmakers would have 30 days to raise objections. Or the administration could bypass the process by declaring an “emergency” requiring immediate shipment, as they’ve done twice recently for Israel.

An Arctic ‘Great Game’ as NATO allies and Russia face off in far north

Hungary, too, may be trying to extract concessions. Like Erdogan, Orban maintains ties to Putin. The Hungarian leader regularly acts as a spoiler of multinational agreements that work against Moscow’s interests, including E.U. sanctions on Russia and aid to Ukraine.

Orban says he takes issue with Swedish criticism that democracy in Hungary has eroded under his rule. But he said the same about Finland, and then quickly dropped his opposition to that country’s entry into NATO when Turkey did.

Russia’s invasion of Ukraine in 2022 has remade the security landscape in Europe, spurring increased defense spending from countries that had been steadily cutting their militaries since the end of the Cold War and reinvigorating NATO after years of questions over the alliance’s relevance.

Sweden had not previously indicated an interest in becoming a full NATO member and had adopted a posture of neutrality and nonalignment in the early 19th century, officially staying on the sidelines during major conflicts, including the world wars.

But while that stance remained central to the country’s self-concept, Sweden gradually strengthened its ties to NATO. It joined the alliance’s Partnership for Peace in 1994, became an “Enhanced Opportunities Partner” in 2014 — after Russia’s annexation of the Crimean Peninsula — and signed a host nation agreement in 2016. Sweden has contributed to NATO-led missions in Bosnia, Kosovo, Afghanistan, Libya and Iraq. As a European Union member since 1995, it is also bound by a mutual defense clause, obligating help if any E.U. member is attacked.

De Vynck and Rauhala reported from Brussels. Karen DeYoung in Washington contributed to this report.