When Russian forces invaded Ukraine in February 2022, one of the first questions asked was whether NATO would intervene. The answer was no — Ukraine is not a NATO member, and the alliance is not obliged to defend it. But the war has revitalised NATO, prompting Finland and Sweden to join, pushing defence spending to record levels, and reminding the world why the alliance was created in the first place. For the UK, NATO is the cornerstone of its defence policy and the reason British troops are stationed from Estonia to the North Atlantic. Here is what NATO is, how it works, and why it matters.
What NATO Is
The North Atlantic Treaty Organization (NATO) is a military alliance of 32 countries (as of 2024) in North America and Europe. It was founded in 1949, in the early years of the Cold War, to counter the Soviet Union and to ensure that the devastation of two world wars would not be repeated.
NATO's founding principle is collective defence: an attack on one member is treated as an attack on all. This is enshrined in Article 5 of the North Atlantic Treaty, the alliance's founding document. The idea is simple: no aggressor would risk attacking a NATO member, knowing it would face the combined military might of the entire alliance.
NATO is not a standing army. Each member maintains its own armed forces, but they train together, share intelligence, and commit to coming to each other's aid if attacked. The alliance is headquartered in Brussels, and its military command structure is led by a Supreme Allied Commander Europe (SACEUR), always a senior US general.
The Members
NATO has grown from 12 founding members in 1949 to 32 today. The original members were the United States, Canada, the UK, France, Belgium, the Netherlands, Luxembourg, Norway, Denmark, Iceland, Italy, and Portugal.
Three waves of expansion followed:
- Cold War expansion — Greece and Turkey joined in 1952, West Germany in 1955, and Spain in 1982.
- Post-Cold War expansion — After the Soviet Union collapsed in 1991, NATO expanded eastward. Poland, Hungary, and the Czech Republic joined in 1999, followed by seven more countries in 2004 (including the Baltic states of Estonia, Latvia, and Lithuania), and Albania and Croatia in 2009.
- Recent expansion — Montenegro joined in 2017, North Macedonia in 2020, and Finland in 2023 and Sweden in 2024, both in response to Russia's invasion of Ukraine.
This expansion has been deeply controversial. Russia sees it as a threat and a betrayal of assurances given (though never formalised) after the Cold War that NATO would not expand eastward. NATO argues that sovereign countries have the right to choose their own alliances, and that NATO is a defensive organisation, not a threat to Russia.
Article 5: Collective Defence
Article 5 is the heart of NATO. It states:
"The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them... will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."
In plain English: if you attack a NATO member, you are at war with all of them.
Article 5 has been invoked only once in NATO's 75-year history: after the 9/11 terrorist attacks on the United States in 2001. NATO members declared that the attacks constituted an armed attack under Article 5, and several countries contributed forces to the US-led war in Afghanistan.
The fact that Article 5 has been invoked only once does not mean it is unimportant. Its deterrent effect is the reason NATO exists. During the Cold War, the Soviet Union never attacked a NATO member, despite decades of tension. The risk of triggering Article 5 — and facing the US nuclear arsenal — was too great.
NATO and the UK
The UK is one of NATO's most important members. It is one of only a handful of countries that meets NATO's target of spending 2% of GDP on defence (the UK spent 2.3% in 2024, according to NATO figures), and it provides significant military capabilities, including:
- Nuclear weapons — The UK is one of three NATO nuclear powers (along with the US and France), operating a fleet of four Vanguard-class submarines armed with Trident II missiles.
- Carrier strike — The UK has two aircraft carriers, HMS Queen Elizabeth and HMS Prince of Wales, which can project power globally.
- Special forces — The UK's Special Air Service (SAS) and Special Boat Service (SBS) are among the world's most capable.
- Intelligence — The UK is a key intelligence partner within NATO, particularly through the Five Eyes alliance with the US, Canada, Australia, and New Zealand.
The UK also hosts NATO forces and infrastructure. RAF Lakenheath in Suffolk is home to US Air Force F-35 fighters, and the UK contributes troops to NATO's Enhanced Forward Presence in Estonia, part of the alliance's effort to deter Russian aggression in the Baltics.
For the UK, NATO is the foundation of its defence policy. The 2021 Integrated Review of Security, Defence, Development and Foreign Policy described NATO as "the cornerstone of Euro-Atlantic security" and committed the UK to being "the leading European Ally within NATO."
NATO and Russia
NATO's relationship with Russia has defined much of its history. During the Cold War, NATO existed to contain the Soviet Union. After the Soviet collapse, NATO tried to build a partnership with Russia, establishing the NATO-Russia Council in 2002 to facilitate dialogue.
That partnership collapsed after Russia's annexation of Crimea in 2014 and its full-scale invasion of Ukraine in 2022. NATO suspended all practical cooperation with Russia, and the alliance has since focused on deterring further Russian aggression.
Russia's objections to NATO expansion are a recurring theme in its propaganda. President Vladimir Putin has repeatedly claimed that NATO's presence in Eastern Europe threatens Russia's security and that the West promised not to expand NATO after German reunification in 1990. Western leaders dispute this, arguing that no such promise was made (and certainly not formalised in a treaty), and that countries have the right to choose their own alliances.
The war in Ukraine has demonstrated the limits of NATO's collective defence. Ukraine is not a member, so Article 5 does not apply. NATO countries have provided billions of pounds in military aid, training, and intelligence, but they have not sent troops or declared war on Russia. The risk of direct NATO-Russia conflict — potentially involving nuclear weapons — is too great.
NATO's 2% Target
At the 2014 NATO summit in Wales, members agreed that those spending less than 2% of GDP on defence should aim to reach that level within a decade. The target was a response to concerns that European members were free-riding on US military power, and that NATO was becoming a two-tier alliance.
As of 2024, 23 of NATO's 32 members meet the 2% target, up from just three in 2014 (the US, UK, and Greece). The war in Ukraine has been a wake-up call, prompting countries like Germany, Poland, and the Baltic states to dramatically increase defence spending.
The UK has consistently met the target, though there are concerns that rising costs and ageing equipment will require further increases. The Ministry of Defence's budget for 2024–25 is £57 billion, the largest in Europe after France.
NATO's Future Challenges
NATO faces several challenges in the coming years:
1. The US commitment
NATO depends on US military power, particularly its nuclear umbrella. But American interest in Europe has waned, and some US politicians (including Donald Trump during his presidency) have questioned whether the US should continue to subsidise European defence. If the US were to withdraw or reduce its commitment, NATO's credibility would be severely damaged.
2. Turkey's role
Turkey is a NATO member but has increasingly pursued its own foreign policy, sometimes at odds with the alliance. It has bought Russian air defence systems, intervened in Syria and Libya, and blocked Sweden's NATO membership for over a year before finally approving it in 2024. Turkey's strategic location (controlling access to the Black Sea) makes it indispensable, but its behaviour is a source of tension.
3. China
NATO's 2022 Strategic Concept, the alliance's guiding document, identified China as a "systemic challenge" for the first time. This reflects growing concern about China's military expansion, its partnership with Russia, and its influence in critical infrastructure in Europe. But NATO members disagree on how to respond, with some (like the US and UK) favouring a tougher line and others (like Germany and France) prioritising economic ties.
4. Defence spending
Despite progress, many NATO members still do not spend enough on defence, and much of what they do spend is wasted on duplicated capabilities and outdated equipment. NATO has called for greater integration and specialisation, but national governments are reluctant to give up sovereignty over their armed forces.
The Bottom Line
NATO is a military alliance of 32 countries committed to collective defence, with Article 5 stating that an attack on one member is an attack on all. It was founded in 1949 to counter the Soviet Union and has expanded eastward since the Cold War, a move Russia cites as a threat. The UK is one of NATO's most important members, spending 2.3% of GDP on defence and providing nuclear weapons, carrier strike, and intelligence capabilities. Article 5 has been invoked only once, after 9/11, but its deterrent effect is the reason NATO exists. The war in Ukraine has revitalised the alliance, prompting Finland and Sweden to join and pushing defence spending to record levels, but NATO faces challenges including the reliability of the US commitment, Turkey's independent foreign policy, and the rise of China. For the UK, NATO is the cornerstone of its defence policy and the guarantee of its security in an increasingly unstable world.