Seventy-five years after it was founded on 4 April 1949 in the wake of World War II, the North Atlantic Treaty Organisation – better known as NATO – is bigger than ever. But allies worry that a rising current of isolationism in American politics could lead to a drop in financial support from the defence alliance's leader.
NATO was born in 1949 out of growing concern over increasing Soviet control over Eastern Europe.
Against the backdrop of a communist coup in Czechoslovakia and Moscow's blockade against West Berlin, 12 countries in Western Europe and North America – wartime allies the United States, Canada, the United Kingdom, Belgium, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway and Portugal – signed the North Atlantic Treaty, NATO's founding document, on 4 April 1949.
The core of the treaty is Article 5, which states that "an armed attack against one or more of them in Europe or North America shall be considered an attack against them all".
That, in turn, triggers the right to individual or collective self-defence.
Effectively, the alliance placed Western Europe under the so-called "nuclear umbrella" of the US, raising the threat of a large-scale nuclear response to any attack.
This – it was assumed – would deter Soviet aggression on the continent.
In response, the USSR created the Warsaw Pact with its satellites Poland, Hungary, East Germany, Czechoslovakia and Bulgaria, and communist allies Romania and Yugoslavia.
France's uneasy NATO membership
France, which hosted NATO for 15 years, always had an uneasy relationship with the alliance.
In 1952 NATO left its temporary offices in London and established a permanent headquarters in Paris, first at the Palais de Chaillot, opposite the Eiffel Tower, and later at purpose-built premises (designed to resemble an A, for "alliance") on the city's western outskirts.
Meanwhile, the US set up its largest military base near Châteauroux, south of Paris.
But in 1966, President Charles de Gaulle withdrew France from NATO's military structure, forcing the closure of American bases.
De Gaulle did not want to surrender France's armed forces to collective control, nor to integrate its nuclear powers. He also demanded the removal of all foreign forces from French territory.
NATO moved its headquarters to Brussels the following year.
France remained a NATO member, however, and continued to participate in the alliance's civil tasks. It eventually rejoined NATO's military command in 2009.
Age of expansion
For 40 years, NATO and the Warsaw Pact maintained a strategic balance during the Cold War.
In 1989 the Berlin Wall fell, and in 1991 the Soviet Union disintegrated. The Warsaw Pact was formally dissolved, effectively removing NATO's original reason for existing.
But the alliance did not cease to exist. In fact, it expanded.
The unification of Germany in 1990 meant that East Germany, a former Warsaw Pact country, joined former West Germany within NATO.
Then, in five waves starting in 1999, NATO expanded eastward, eagerly incorporating all former Warsaw Pact countries except Russia itself.
In 2004, four years after Vladimir Putin became Russia's paramount leader, NATO saw its biggest expansion since its founding, integrating Bulgaria, Romania, Slovakia, Slovenia and the three Baltic states – Estonia, Latvia and Lithuania – into its ranks.
The move is thought to have angered Putin, especially since the Baltic states had belonged to the USSR itself.
'Serious provocation'
Relations between Putin and the NATO countries were initially courteous: the NATO-Russia Council was established in 2001, and Russia and the alliance engaged in joint military exercises, and Russia's membership expanded the G7 into the G8.
Six years later, Putin was no longer prepared to play nice. Most of the former Warsaw Pact bloc was now integrated into NATO and in a speech at the 2007 Munich Security Conference, Putin scolded NATO for having "put its front line forces on our borders", declaring that the expansion "does not have any relation with the modernisation of the alliance itself or with ensuring security in Europe".
He branded NATO a "serious provocation that reduces the level of mutual trust".
Washington and its NATO partners hardly took notice of the implicit warning.
Things escalated when former Soviet Union republics Georgia and Ukraine started to show interest in possible NATO membership.
Increased Russian aggression against Georgia in 2008 and Ukraine from 2014 made NATO partners hesitate to ever seriously consider letting them in, fearing being pulled into a direct confrontation with Moscow.
Stronger than ever?
The entry of Russian armed forces into Ukraine in February 2022 and the ensuing conflict prompted two formerly non-aligned countries, Finland and Sweden, to fast-track themselves into NATO.
Finland joined on 4 April 2023 and Sweden on 7 March 2024, after hurdles mounted by Hungary and Turkey were cleared.
With 32 member states, NATO is now larger and stronger than ever.
But with a possible re-election of NATO-sceptic Donald Trump as US president in November, the other members fear that Washington's financial support and leadership over the alliance may not be guaranteed much longer.
