After stalling the process of Sweden joining NATO due to Turkey's concerns about the country harboring PKK members, President Erdoğan has given the green light for the Northern European country's accession to the military alliance. Speculations as to why the Turkish president changed course on such short notice are manifold. The most plausible reasons include reopening up talks about Turkey joining the EU, the U.S. providing the country with F-16 fighter jets and easier access to EU visas for Turkish citizens.
In April, Finland became the latest member of the military alliance comprised of 29 European nations, Canada and the United States. Finland's accession roughly doubled NATO's border with Russia, which threatened to take "counter-measures" and described the accession as an "encroachment on Russia's security and national interests."
Even before the outbreak of the war, Russian President Vladimir Putin has repeatedly brought up the topic of NATO, the European-North American military alliance, in connection with Ukraine. The country is currently one of three nations with a declared aspiration to join the treaty, having officially applied for fast-track accession in September 2022.
NATO's eastward expansion has been a thorn in Putin’s side for a long time. “Any further NATO movement to the east is unacceptable", Putin said in December 2021, two months before the invasion of Ukraine began. "Putin wanted less NATO along his borders," NATO Secretary General Jens Stoltenberg said in a statement ahead of Finland formally joining NATO in April. "He is getting exactly the opposite. He is getting more troops, more readiness, more forces, land, sea and air in the eastern part of the Alliance. And he is getting more members."
NATO’s declared open door policy included in its founding treaty is generally making membership an option for European sovereign nations. The organization that started out in 1949 among 12 nations has since then attracted new members, especially in the past two decades, from Eastern Europe and the Balkans.