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

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.”