Finland's NATO membership received the green light from Turkey's parliament on Thursday, paving the way for the country to become the Western defence alliance's newest member. NATO has an open-door policy, meaning that any country can be invited to join if it expresses an interest, as long as it is able and willing to uphold the principles of the bloc's founding treaty. However, under the accession rules, any member state can veto a new country from joining. Turkey and Hungary had been stalling the process of Finland and Sweden joining NATO, but Hungary has since softened its stance on Finland's accession, opening the door to its membership earlier this month.

Turkey remains opposed to Sweden joining, stating that it will not approve Sweden's NATO membership unless the country extradites “terrorists” upon Turkish request. However, Sweden has made clear this is not an option. Turkish President Erdogan has disagreed with NATO allies on a number of issues, including Syria and Libya, and opposed the appointment of Denmark's Anders Fogh Rasmussen as head of NATO, until then-US President Barack Obama pledged that one of Rasmussen's deputies would be a Turk. While Turkey has now ratified Finland's NATO membership, the country's unwillingness to allow Sweden's accession risks leaving it isolated, as it remains the sole NATO member blocking the country's access to the alliance.