Finland to join NATO on Tuesday. What will it take for Sweden to follow?

Finland on Tuesday is set to become the 31st member of the North Atlantic Treaty Organization (NATO), the largest military alliance in the world.

The historic moment comes after Turkey last week decided to allow Finland to move ahead on joining NATO without its neighbor Sweden.

NATO Secretary General Jens Stoltenberg on Monday said it was “a historic week” as the alliance “will raise the Finnish flag for the first time here at the NATO headquarters,” marking “a good day for Finland’s security, for Nordic security, and for NATO as a whole.”

He also said that he hopes Sweden will join NATO in coming months, though that seems far from certain.

All members of the alliance must approve any new members, and Turkey has put the hold on Stockholm’s bid in what experts view as a power play by Turkish President Recep Tayyip Erdoğan.

“This is the nerve-wracking part, that it’s really not clear what the timeline is,” said Elisabeth Braw, an expert on European defense issues at the American Enterprise Institute. “To a large part it’s about political theater, which makes it so unpredictable.”

Here’s how the process works, how Finland got through and what’s ahead for Sweden.

The process so far

Finland and Sweden for decades have kept a stance of non-alignment with NATO to avoid tensions with Russia, which sees the alliance’s expansion as a security threat. Finland shares an 830-mile border with Russia.

But after Russian President Vladimir Putin’s unprovoked attack on Ukraine last year, the two Nordic countries quickly ditched their neutral status and applied for NATO membership in May.

Helsinki and Stockholm later that summer were formally invited to join the alliance, with most NATO members approving their applications within weeks.

Under the accession rules, however, any member can veto a new country from joining, and Turkey and Hungary stalled the process.

Ankara insisted Finland and Sweden take a tougher stance against the Kurdistan Workers’ Party (PKK), considered a terror group by Turkey and the European Union.

The three countries took halting steps toward a compromise — in June signing a memorandum of understanding to address concerns by Ankara — and last week Turkey’s parliament unanimously ratified Finland’s accession to NATO, the last member country to do so.

What’s next for Sweden? 

Western officials have expressed optimism that Sweden will soon join its Nordic neighbor in entering NATO, preferably ahead of a leaders summit set for July in Vilnius, Lithuania.

But Turkey has not indicated whether it will approve Sweden’s NATO membership, which has been stalled since January.

And Hungary, the second-to-last NATO member to approve Finland’s accession, found there to be “an ample amount of grievances that need to be addressed” before it ratifies Sweden’s bid, government spokesperson Zoltán Kovács said last week, as reported by Reuters.

Speaking to reporters last week, Principal Deputy Assistant Secretary for European and Eurasian affairs Dereck Hogan said U.S. officials “want both Hungary as well as Turkey to move forward with Sweden’s accession just as soon as possible … certainly by Vilnius to have all of this wrapped up, if not sooner.”

He added that Secretary of State Antony Blinken, who will be in Brussels on Tuesday for Finland’s accession, will meet with his Turkish counterpart on NATO expansion, a major “subject of our public as well as private engagements.”

Also keeping things up in the air is Turkey’s presidential elections in May. Many have speculated that Erdoğan is purposely holding back support for Sweden due to domestic political reasons ahead of votes.

“I think this is a win-win situation for him, especially at a crucial time a few weeks before the presidential elections,” said Mathieu Droin, a NATO expert with the Center for Strategic and International Studies think tank. “It helps Erdoğan to present himself as a magnanimous leader.”

Hungary, meanwhile, has never made its demands clear, with Prime Minister Viktor Orban accusing Stockholm and Helsinki of spreading “outright lies” about his country.

Still, even if talks continue to drag out for Sweden, it doesn’t mean the country will be any less safe, according to Droin.

“I think it doesn’t change dramatically the security landscape,” he told The Hill. “Sweden has already been very close to NATO [and] in the past few years has integrated even closer. It’s also fair to remember that there have been security warranties given by other NATO allies to Sweden, but also the European Union.”

How Russia has reacted 

News of Finland’s impending membership did not appear to sit well with Russia, which this week pledged to boost its own defenses near the countries’ shared border should NATO send any troops into the Nordic nation.

“We will strengthen our military potential in the west and in the northwest,” Russia’s Deputy Foreign Minister Alexander Grushko said on the state-controlled RIA Novosti news agency, as reported by The Associated Press.

“In case of deployment of forces of other NATO members on the territory of Finland, we will take additional steps to ensure Russia’s military security.”

For the latest news, weather, sports, and streaming video, head to The Hill.