ISTANBUL — Since Finland announced its intention to join NATO last year after Russia’s full-scale invasion of Ukraine, one of the largest boulders obstructing its path was the will of one man: President Recep Tayyip Erdogan of Turkey.
Each member of the alliance must approve the acceptance of any new NATO member, a setup that gave Mr. Erdogan the ability to flout the wishes of his NATO allies. And flout those wishes he did, saying that Turkey would only accept Finland and Sweden, which had hoped to join the alliance together, if they fulfilled Turkey’s conditions.
Turkey demanded that they do more to fight what Turkey considered terrorist activity inside their borders, largely meaning cracking down on Kurdish activists and members of a religious organization that Turkey accuses of organizing a failed coup against Mr. Erdogan in 2016.
Officials from other NATO countries considered those demands unreasonable, and critics accused Mr. Erdogan of abusing the alliance’s rules for domestic political gain.
But it worked, to some extent. Finland tightened its counterterrorism legislation, and Sweden has extradited at least one person requested by the Turks, although the Swedish courts have blocked many others.
All along, Turkey’s demands for Finland were less than those for Sweden, and Mr. Erdogan said earlier this month that Turkey would accept Finland into NATO separately from Sweden. The vote on Thursday in the Turkish Parliament made that move official.
It remains unclear when Turkey could take the same step for Sweden.
Mr. Erdogan’s obstruction of NATO damaged his standing in Washington and other NATO capitals, said Gonul Tol, the director of the Turkey program at the Middle East Institute, a think tank and cultural center, in Washington.
Sentiment toward Mr. Erdogan, who has long had a tendentious relationship with the United States, warmed slightly in Washington after he condemned Russia’s invasion of Ukraine and closed the Turkish straights to most military traffic, complicating Russian naval maneuvers, she said.
“But the minute Erdogan starting using Finland and Sweden as cards, I think he lost that good will,” Ms. Tol said, adding that instead of celebrating the alliance’s enlargement, Turkey’s NATO allies are now asking, “Why did we have to wait for so long?”
If Mr. Erdogan benefited at all, it was likely inside Turkey, where he is seeking another term in a presidential election scheduled for May 14. A range of polls indicate that he could lose to the joint candidate of a coalition of opposition parties, largely because of voter frustration with his handling of the economy and his government’s response to a devastating earthquake on Feb. 6 that killed more than 50,000 people in Turkey.
Still, many of Mr. Erdogan’s supporters like to see him exerting his power on the world stage as he did by stalling the expansion of NATO, Ms. Tol said.
“Erdogan uses that tough man image, the man who gets things done, who brings the world to his feet,” she said. “He needs that image more than ever now because he is kind of weak.”