This week marks 75 years of the largest peacetime military alliance in the world.
The North Atlantic Treaty Organisation, which you will likely know as NATO, was formed on 4 April 1949.
At the time it was an alliance of 12 countries. Now it has expanded to 32, with Sweden becoming its most recent member.
In the aftermath of the Second World War, European nations were struggling to rebuild their economies and were concerned about their security.
There were also growing fears of Soviet expansionism. Soviet leader Joseph Stalin had installed his leadership and communist governments in most Eastern European countries by 1949.
This left smaller countries in Europe more vulnerable to both Soviet influences and attack.
The US – which by then had turned its back on its traditional policy of diplomatic isolationism – became concerned this could lead to communism becoming the dominant force across the world.
The States was providing aid through the Marshall Plan to help Europe’s economic stabilisation, but European countries still wanted more confidence in their security.
US officials feared Western European countries might deal with their security concerns by negotiating with the Soviets.
The need for a defensive organisation was particularly highlighted by the Berlin Blockade of 1948.
This was an attempt by the Soviet Union to limit the ability of the US, UK and France to travel to their sectors of the city of Berlin, which at the time lay inside Russian-occupied East Germany.
The Soviets blocked all rail, road and canal access to the western zones of Berlin, leaving 2.5 million people with no access to food, medicine, fuel, electricity and other basic goods.
Western powers were forced to airlift supplies to West Berlin for nearly a year.
The administration of US president Harry Truman decided a European-American military alliance would boost security in western Europe.
It would mean the US could place weapons in member states, making it easier to fend off any potential attack.
Following much discussion and debate, the North Atlantic Treaty was signed in 1949.
The US, Canada, Belgium, Denmark, France, Iceland, Italy, Luxemburg, the Netherlands, Norway, Portugal and the UK were the original signatories.
They agreed to consult each other about threats and defence matters, and most importantly agreed that any armed attack against one member “shall be considered an attack against them all”.
Following such an attack, each ally will take “such action as it deems necessary, including the use of armed force” in response.
NATO has said it is only partially true that it was formed in response to the threat from the Soviet Union.
“In fact, the alliance’s creation was part of a broader effort to serve three purposes: deterring Soviet expansionism, forbidding the revival of nationalist militarism in Europe through a strong North American presence on the continent, and encouraging European political integration,” it says on its website.
