As Finland and Sweden head down the path toward membership in the North Atlantic Treaty Organization, Turkey could pose a major hurdle. In order to gain entry into the 30-member military alliance, all countries must approve new applicants.

Turkish President Recep Tayyip Erdogan reiterated his concern this week, claiming the two countries refuse to extradite "terrorists". Turkey accuses Sweden and Finland of harboring members of the Kurdistan Workers' Party (PKK) which it views as a terrorist organization. Swedish officials deny the accusation and say they will send diplomats to Turkey to discuss further. 

The Turkish comments strike a very different chord from the rest of the group. Nearly all members support the expansion, including the U.S. "The United States would strongly support the NATO application by either Sweden or Finland should they choose to formally apply to the alliance. We will respect whatever decision they make," commented Secretary of State Antony Blinken

NATO secretary general stoltenberg

NATO Secretary General Jens Stoltenberg, center, participates in a media conference with Finland's Foreign Minister Pekka Haavisto, left, and Sweden's Foreign Minister Ann Linde, right, at NATO headquarters in Brussels on Jan. 24. (AP/Olivier Matthys, File)

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Why did Finland and Sweden not join NATO previously? 

Historically, the two Nordic countries have taken stances of military non-alignment however the threat of war on European soil has prompted world leaders to reevaluate relationships. 

Finland shares more than 800 miles of border with Russia. Finland’s President Sauli Niinistö and Prime Minister Sanna Marin announced the country would officially seek to join the group. "NATO membership would strengthen Finland's security. As a member of NATO, Finland would strengthen the entire defense alliance," the two leaders communicated in a joint statement last week. Public support for a NATO membership always polled around 25% in Finland before Russia’s invasion of Ukraine in February 2022. Since the outbreak of war on their doorsteps, recent surveys suggest nearly 80% of the Finnish population supports joining the alliance. 

In Sweden, there’s currently broad support to join NATO. "The best thing for the security of Sweden and the Swedish people is to join Nato," said Swedish Prime Minister Magdalena Andersson. The PM also warned her citizens the application would prompt a response from Moscow.

Biden in Brussels

President Biden speaking during a media conference, after a NATO summit and Group of Seven meeting, at NATO headquarters in Brussels (AP Photo/Markus Schreiber, File)

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How has Russia responded? 

The Kremlin has repeatedly warned that a NATO expansion would warrant both military and technical countermeasures. On Tuesday, the Russian Foreign Ministry announced it was expelling two Finnish diplomats from the country.

"Sweden’s accession to NATO will inflict considerable damage to the security of Northern Europe and Europe as a whole," the Russian Foreign Ministry said in a statement. 

When and why was NATO formed? 

NATO was formed in 1949 as an alliance against the Soviet Union at the time. The 12 original founders include Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom and the United States. 

The group has since expanded to include 30 members with a shared purpose of political solidarity and military defense. The Article 5 clause guarantees that protection, "An attack against one is an armed attack against all". 

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Who can join? 

Countries seeking to join the world’s biggest military alliance must meet specific criteria. These nations must be in good standing with current members, have a functioning democratic political system based on a market economy, hold the capability to make military contribution to NATO operations, have fair treatment of minority populations, and pledge to resolve conflicts peacefully. 

What happens next? 

Finland and Sweden are already NATO’s closest partners. In a 188-8 vote on Tuesday, the Finnish parliament voted to seek membership. At the same time, Sweden signed a formal application.

In order to join, a formal request must be submitted before NATO can assess the request.  NATO Secretary General Jens Stoltenberg said he predicts the process could happen "quite quickly". Typically, however, the application timeline can last roughly one year. 

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In the meantime, Norway, Denmark, and Iceland say they will support Sweden and Finland. The U.S. and Germany have provided security assurances. British Prime Minister Boris Johnson has also given security guarantees, promising to defend both countries if they come under attack. 

President Biden is set to meet with the leaders of Sweden and Finland this week. "The leaders will discuss Finland’s and Sweden’s NATO applications and European security, as well as strengthening our close partnerships across a range of global issues and support for Ukraine," said White House Press Secretary Karine Jean-Pierre.