Sweden became NATO’s newest member, upon depositing its instrument of accession to the North Atlantic Treaty with the government of the United States in Washington DC.

Sweden’s flag was raised alongside those of the other 31 allies in a ceremony at Allied Command Transformation, NATO’s Strategic Warfare Development Command, and simultaneously at NATO headquarters in Brussels and at NATO commands across Europe.

Sweden set aside decades of post-World War II neutrality when it formally joined NATO. The neighbouring nation of Finland had already joined in April 2023 in another historic move ending years of military non-alignment.

NATO requires the unanimous approval of all existing members to expand, and Turkey and Hungary were the only countries that have been holding out.

For NATO, the accessions of Sweden and Finland — which shares a 1,340-km border with Russia — are the most significant additions in decades. 

It is also a blow for Russian President Vladimir Putin, who has sought to  prevent any further strengthening of the alliance.

Sweden’s membership completes a strategic ring of NATO territory around the Baltic Sea. The country now benefits from the alliance’s collective security guarantee — Article 5 of its treaty — a vow that an attack on one of them will be met by a response from them all.

What is NATO?

• North Atlantic Treaty Organisation (NATO) was formed in 1949 with the signing of the Washington Treaty. 

• NATO is a security alliance of 32 countries from North America and Europe. 

• In 1949, there were 12 founding members of the alliance: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom and the United States. 

• The other member countries are: Greece and Turkey (1952), Germany (1955), Spain (1982), the Czech Republic, Hungary and Poland (1999), Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia (2004), Albania and Croatia (2009), Montenegro (2017), North Macedonia (2020), Finland (2023) and Sweden (2024).

• NATO’s fundamental goal is to safeguard the Allies’ freedom and security by political and military means.

• NATO enables members to consult and cooperate on defence and security-related issues to solve problems, build trust and, in the long run, prevent conflict.

• NATO is committed to the peaceful resolution of disputes. If diplomatic efforts fail, it has the military power to undertake crisis-management operations. These are carried out under the collective defence clause of NATO’s founding treaty — Article 5 of the Washington Treaty or under a United Nations mandate, alone or in cooperation with other countries and international organisations.

Why Sweden and Finland decided to join NATO?

• Once a regional military power, Sweden has avoided military alliances since the end of the Napoleonic Wars. Like Finland it remained neutral throughout the Cold War, but formed closer relations with NATO after the 1991 Soviet collapse. 

• After being firmly against NATO membership for decades, public opinion in both countries shifted following Russia’s invasion of Ukraine in February 2022.

• Sweden and Finland abandoned their traditional positions of military non-alignment to seek protection under NATO's security umbrella,  

• The Swedish and Finnish governments swiftly initiated discussions across political parties about NATO membership and reached out to the US, Britain, Germany and other NATO countries for their support.

• Finland joined the alliance in April 2023, becoming NATO’s 31st member, after Turkey’s Parliament ratified the Nordic country’s bid.