MADRID — NATO leaders on Wednesday formally invited Finland and Sweden to join the alliance, one day after Turkey dropped its objections to their membership, clearing the way for what would be one of the most significant expansions of the alliance in decades.
The historic deal, following Turkey’s agreement to a memorandum with the two Nordic countries, underscores how the war in Ukraine has backfired for President Vladimir V. Putin, subverting Russian efforts to weaken NATO and pushing Sweden and Finland, which were neutral and nonaligned for decades, into the alliance’s arms.
After weeks of talks, capped by an hourslong meeting in Madrid, President Recep Tayyip Erdogan of Turkey agreed to lift his block on Sweden and Finland’s membership in return for a set of actions and promises that they will act against terrorism and terrorist organizations.
“As NATO allies, Finland and Sweden commit to fully support Turkey against threats to its national security,” NATO’s secretary general, Jens Stoltenberg, said, providing some details of the agreement. “This includes further amending their domestic legislation, cracking down on P.K.K. activities and entering into an agreement with Turkey on extradition,” he added, referring to the Kurdistan Workers’ Party, which seeks an independent Kurdish state on territory partly within Turkey’s borders.
Mr. Stoltenberg confirmed at a news conference on Wednesday that the alliance had formally invited Finland and Sweden to join after Turkey lifted its objections on Tuesday night. Now, the legislatures of all 30 current members must ratify the accession, which could take several months.
Better Understand the Russia-Ukraine War
- History and Background: Here’s what to know about Russia and Ukraine’s relationship and the causes of the conflict.
- How the Battle Is Unfolding: Russian and Ukrainian forces are using a bevy of weapons as a deadly war of attrition grinds on in eastern Ukraine.
- Russia’s Brutal Strategy: An analysis of more than 1,000 photos found that Russia has used hundreds of weapons in Ukraine that are widely banned by international treaties.
- Outside Pressures: Governments, sports organizations and businesses are taking steps to punish Russia. Here are some of the sanctions adopted so far and a list of companies that have pulled out of the country.
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The U.S. Senate is already pressing ahead with hearings on the application, and Mr. Biden has been a firm proponent of the new members.
Mr. Erdogan had been blocking the Nordic countries’ NATO bids amid concerns over Sweden’s longtime support for the P.K.K., which has attacked nonmilitary targets and killed civilians in Turkey, is outlawed in that country and is designated by both the United States and the European Union as a terrorist organization.
But the memorandum does not specify the extradition of any of the 45 people or so Mr. Erdogan wanted sent to Turkey to face trial on terrorism charges. Sweden has already passed tougher legislation against terrorism that goes into effect on Friday.
Both Finland and Sweden had been militarily nonaligned for many years, but decided to apply to join the alliance after Russia invaded Ukraine in February. With Russia attacking a neighbor, both countries felt vulnerable, though Sweden, with a long tradition of neutrality, was more hesitant.
Mr. Putin warned both countries against joining NATO, but his threats proved counterproductive.
The two countries bring geostrategic benefits to the alliance. Finland shares an 830-mile border with Russia and has a well-equipped modern army; Sweden can control the entrance to the Baltic Sea, which will help a great deal in NATO planning to defend the more vulnerable countries in Eastern Europe.
The final push to resolve the dispute started early Tuesday, when President Biden called Mr. Erdogan to urge him to “seize the moment” on the eve of the summit, to allow discussions on other topics to proceed, according to a senior administration official with knowledge of the discussion.
The official said that the deal between Turkey and the two Nordic countries involved compromises on both sides, including the statement by Turkey welcoming Finland and Sweden to apply and issues involving an arms embargo imposed on Turkey and Turkey’s belief that Finland and Sweden had offered safe havens to groups they considered terrorists.
Johanna Lemola contributed reporting from Helsinki, Finland.
