What Is the North Atlantic Treaty Organization (NATO)?

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The North Atlantic Treaty Organization is a military alliance of countries from Europe and North America promising collective defense. Currently numbering 30 nations, NATO was formed initially to counter the communist East and has searched for a new identity in the post-Cold War world.


In the aftermath of the Second World War, with ideologically opposed Soviet armies occupying much of Eastern Europe and fears still high over German aggression, the nations of Western Europe searched for a new form of military alliance to protect themselves. In March 1948 the Brussels Pact was signed between France, Britain, Holland, Belgium and Luxembourg, creating a defence alliance called the Western European Union, but there was a feeling that any effective alliance would have to include the US and Canada.

In the US there was widespread concern about both the spread of Communism in Europe – strong Communist parties had formed in France and Italy - and potential aggression from Soviet armies, leading the US to seek talks about an Atlantic alliance with the west of Europe. The perceived need for a new defensive unit to rival the Eastern bloc was exacerbated by the Berlin Blockade of 1949, leading to an agreement that same year with many nations from Europe. Some nations opposed membership and still do, e.g. Sweden, Ireland.

Creation, Structure, and Collective Security

NATO was created by the North Atlantic Treaty, also called the Washington Treaty, which was signed on April 5th 1949. There were twelve signatories, including the United States, Canada and Britain (full list below). The head of NATO's military operations is the Supreme Allied Commander Europe, a position always held by an American so their troops don’t come under foreign command, answering to the North Atlantic Council of ambassadors from member nations, which is led by the Secretary General of NATO, who is always European. The centrepiece of the NATO treaty is Article 5, promising collective security:

"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, in exercise of the right of individual or collective self-defense recognized by Article 51 of the Charter of the United Nations, 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."

The German Question

The NATO treaty also allowed for the alliance’s expansion among European nations, and one of the earliest debates among NATO members was the German question: should West Germany (the East was under rival Soviet control) be re-armed and allowed to join NATO. There was opposition, invoking the recent German aggression which caused World War Two, but in May 1955 Germany was allowed to join, a move which caused upset in Russia and led to the formation of the rival Warsaw Pact alliance of Eastern communist nations.

NATO and the Cold War

NATO had, in many ways, been formed to secure West Europe against the threat of Soviet Russia, and the Cold War of 1945 to 1991 saw an often tense military standoff between NATO on one side and the Warsaw Pact nations on the other. However, there was never a direct military engagement, thanks in part to the threat of nuclear war; as part of NATO agreements nuclear weapons were stationed in Europe. There were tensions within NATO itself, and in 1966 France withdrew from the military command established in 1949. Nevertheless, there was never a Russian incursion into the western democracies, in large part due to the NATO alliance. Europe was very familiar with an aggressor taking one country after another thanks for the late 1930s and did not let it happen again.

NATO After the Cold War

The end of the Cold War in 1991 led to three major developments: the expansion of NATO to include new nations from the former Eastern bloc (full list below), the re-imagining of NATO as a ‘co-operative security’ alliance able to deal with European conflicts not involving member nations and the first use of NATO forces in combat. This first occurred during the Wars of the Former Yugoslavia, when NATO used air-strikes first against Bosnian-Serb positions in 1995, and again in 1999 against Serbia, plus the creation of a 60,000 peace keeping force in the region.

NATO also created the Partnership for Peace initiative in 1994, aimed at engaging and building trust with ex-Warsaw Pact nations in Eastern Europe and the former Soviet Union, and later the nations from the Former Yugoslavia. As of 2020, there are 30 full members of NATO, along with a handful of aspiring member states and non-member partner states.

NATO and the War on Terror:

The conflict in the former Yugoslavia had not involved a NATO member state, and the famous clause 5 was first – and unanimously - invoked in 2001 after terrorist attacks on the United States, leading to NATO forces running peace-keeping operations in Afghanistan. NATO has also created the Allied Rapid Reaction Force (ARRF) for faster responses. However, NATO has come under pressure in recent years from people arguing it should be scaled down, or left to Europe, despite the increase in Russian aggression in the same period. NATO might still be searching for a role, but it played a huge role in maintaining the status quo in the Cold War, and has potential in a world where Cold War aftershocks keep happening. 

Member States

1949 Founder Members: Belgium, Canada, Denmark, France (withdrew from military structure 1966), Iceland, Italy, Luxembourg, The Netherlands, Norway, Portugal, United Kingdom, United States
1952: Greece (withdrew from military command 1974 – 80), Turkey
1955: West Germany (With East Germany as reunified Germany from 1990)
1982: Spain
1999: Czech Republic, Hungary, Poland
2004: Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, Slovenia
2009: Albania, Croatia
2017: Montenegro

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Wilde, Robert. "What Is the North Atlantic Treaty Organization (NATO)?" ThoughtCo, Apr. 5, 2023, thoughtco.com/what-is-nato-1221961. Wilde, Robert. (2023, April 5). What Is the North Atlantic Treaty Organization (NATO)? Retrieved from https://www.thoughtco.com/what-is-nato-1221961 Wilde, Robert. "What Is the North Atlantic Treaty Organization (NATO)?" ThoughtCo. https://www.thoughtco.com/what-is-nato-1221961 (accessed June 6, 2023).