75 years of NATO: The North Atlantic Treaty Organization explained

This article was first published in July 2022 and most recently updated in July 2024.

This year marks 75 years since the conception of the North Atlantic Treaty Organization (NATO), a political and military alliance currently made up of 32 countries.

Heads of state from member countries marked the occasion at a summit in Washington DC in July 2024. The summit agenda, NATO officials said, includes the wide variety of issues facing the Alliance such as the war in Ukraine and deterrence mechanisms.

Ahead of the gathering, NATO Secretary General Jens Stoltenberg stated that NATO is "not only the most successful and strongest, but also the longest-lasting Alliance in history," adding that "we are stronger and safer together, in NATO."

In March 2024, Sweden officially joined NATO as the 32nd Ally, in what Stoltenberg described as a "historic day".

"Sweden will now take its rightful place at NATO’s table, with an equal say in shaping NATO policies and decisions," Stoltenberg said."Sweden’s accession makes NATO stronger, Sweden safer and the whole Alliance more secure. Today’s accession demonstrates that NATO’s door remains open and that every nation has the right to choose its own path.”

Two days after the second anniversary of the Russian invasion of Ukraine, the final hurdle in Sweden's path to joining the world's most powerful military bloc was cleared, as Hungary approved its accession.

"Sweden is leaving 200 years of neutrality and military non-alignment behind," Prime Minister Ulf Kristersson told a press conference. "We are joining NATO in order to defend what we are and everything we believe in even better. We are defending our freedom, our democracy and our values, together with others."

It comes less than a year after Sweden's neighbour, Finland, joined in April 2023, marking the biggest expansion of NATO since members joined from eastern Europe after the collapse of the Soviet Union in 1991.

Russia's invasion of Ukraine in 2022 prompted Sweden to abandon its non-alignment policy and seek greater security within NATO.

Ukraine itself formally submitted an application to join the bloc in September 2022 and President Volodymyr Zelenskiy received assurances at the Vilnius Summit in the Lithuanian capital in July 2023, where Allies reconfirmed their commitment to make Ukraine a member.

Risks officers surveyed for the World Economic Forum's Global Risks Report 2024 said "interstate armed conflict" was one of the top five most severe risks facing the world in the short term.

The Vilnius Summit also included the inaugural session of the NATO-Ukraine Council on 12 July, where Zelenskiy was welcomed by Stoltenberg.

He said: ''We stand with you in your courageous struggle for freedom and sovereignty ... We need to keep up and further expand our support to help Ukraine liberate its land and deter future Russian aggression.

"At this Summit, we have reaffirmed that Ukraine will become a member of the Alliance and we have made decisions to bring Ukraine closer to NATO. Today we meet as equals. And I look forward to the day we meet as Allies."

Meanwhile, the G7 countries unveiled a new framework to boost Ukraine's long-term security and defences against Russia.

US President Joe Biden said: "NATO is stronger, more energized and, yes, more united than ever in its history. Indeed, more vital to our shared future."

Sweden's road to membership of NATO has been a long one. In July 2023, the country's bid to join NATO was finally approved by Türkiye, which had been blocking its application pending Sweden recognizing rebel groups as terrorist organizations.

On 10 July, NATO said: "Sweden has amended its constitution, changed its laws, significantly expanded its counter-terrorism cooperation against the PKK, and resumed arms exports to Türkiye, all steps set out in the Trilateral Memorandum agreed in 2022."

Both Sweden, and Finland, which has a 1,340km border with Russia, dropped their traditional stance of neutrality and applied to join NATO after the Russian invasion of Ukraine.

In June 2022, a declaration from the 30 members of NATO, formally invited the two countries to join, while also naming the Russian Federation as “the most significant and direct threat to Allies’ security and to peace and stability in the Euro-Atlantic area” – and reiterating “unwavering support” for Ukraine.

Finland officially became the 31st Ally of NATO in April 2023, after NATO Allies signed its Accession Protocol on 5 July, 2022. All 30 national parliaments had voted to ratify the country’s membership.

NATO’s history is tied to Russian expansionism. It was created in 1949, in response to then premier of the USSR Joseph Stalin’s attempts to bring other states under communist rule.

The US, Canada, the UK, Belgium, Denmark, France, Iceland, Italy, Luxemburg, the Netherlands, Norway and Portugal signed a treaty stating that “an armed attack against one or more … shall be considered an attack against them all”.

It has since gone through nine rounds of enlargement: by the fall of the Berlin wall in 1989, there were 16 countries and in the 1990s, after the collapse of the USSR, former Soviet countries began joining, taking the total up to 30. Now that Sweden has officially joined, the number of Allies totals 32.

The Madrid Summit Declaration in June 2022, reaffirmed NATO’s open-door policy, which allows any European country to apply to join, but they must commit to defence spending of 2% of GDP.

In March 2020, the previous round of enlargement saw the Republic of North Macedonia join, while Georgia, Bosnia and Herzegovina are in the application process, now alongside Ukraine.