Map - NATO

The North Atlantic Treaty Organization (NATO, ; Organisation du traité de l'Atlantique nord, OTAN), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two North American. Established in the aftermath of World War II, the organization implemented the North Atlantic Treaty, signed in Washington, D.C., on 4 April 1949. NATO is a collective security system: its independent member states agree to defend each other against attacks by third parties. During the Cold War, NATO operated as a check on the perceived threat posed by the Soviet Union. The alliance remained in place after the dissolution of the Soviet Union and has been involved in military operations in the Balkans, the Middle East, South Asia, and Africa. The organization's motto is animus in consulendo liber (Latin for "a mind unfettered in deliberation").

NATO's main headquarters are located in Brussels, Belgium, while NATO's military headquarters are near Mons, Belgium. The alliance has targeted its NATO Response Force deployments in Eastern Europe, and the combined militaries of all NATO members include around 3.5 million soldiers and personnel. Their combined military spending constituted over 57 percent of the global nominal total. Moreover, members have agreed to reach or maintain the target defence spending of at least two percent of their GDP by 2024.

NATO formed with twelve founding members and has added new members eight times, most recently when North Macedonia joined the alliance in March 2020. Following the acceptance of their applications for membership in June 2022, Finland and Sweden are anticipated to become the 31st and 32nd members, with their Accession Protocols to the North Atlantic Treaty now in the process of being ratified by the existing members. In addition, NATO currently recognizes Bosnia and Herzegovina, Georgia, and Ukraine as aspiring members. Enlargement has led to tensions with non-member Russia, one of the twenty additional countries participating in NATO's Partnership for Peace programme. Another nineteen countries are involved in institutionalized dialogue programmes with NATO.

The Treaty of Dunkirk was signed by France and the United Kingdom on 4 March 1947, during the aftermath of World War II and the start of the Cold War, as a Treaty of Alliance and Mutual Assistance in the event of possible attacks by Germany or the Soviet Union. In March 1948, this alliance was expanded in the Treaty of Brussels to include the Benelux countries, forming the Brussels Treaty Organization, commonly known as the Western Union. Talks for a wider military alliance, which could include North America, also began that month in the United States, where their foreign policy under the Truman Doctrine promoted international solidarity against actions they saw as communist aggression, such as the February 1948 coup d'état in Czechoslovakia. These talks resulted in the signature of the North Atlantic Treaty on 4 April 1949 by the member states of the Western Union plus the United States, Canada, Portugal, Italy, Norway, Denmark, and Iceland. Canadian diplomat Lester B. Pearson was a key author and drafter of the treaty.

The North Atlantic Treaty was largely dormant until the Korean War initiated the establishment of NATO to implement it with an integrated military structure. This included the formation of Supreme Headquarters Allied Powers Europe (SHAPE) in 1951, which adopted many of the Western Union's military structures and plans, including their agreements on standardizing equipment and agreements on stationing foreign military forces in European countries. In 1952, the post of Secretary General of NATO was established as the organization's chief civilian. That year also saw the first major NATO maritime exercises, Exercise Mainbrace and the accession of Greece and Turkey to the organization. Following the London and Paris Conferences, West Germany was permitted to rearm militarily, as they joined NATO in May 1955, which was, in turn, a major factor in the creation of the Soviet-dominated Warsaw Pact, delineating the two opposing sides of the Cold War.

The building of the Berlin Wall in 1961 marked a height in Cold War tensions, when 400,000 US troops were stationed in Europe. Doubts over the strength of the relationship between the European states and the United States ebbed and flowed, along with doubts over the credibility of the NATO defence against a prospective Soviet invasion – doubts that led to the development of the independent French nuclear deterrent and the withdrawal of France from NATO's military structure in 1966. In 1982, the newly democratic Spain joined the alliance.

The Revolutions of 1989 in Europe led to a strategic re-evaluation of NATO's purpose, nature, tasks, and focus on the continent. In October 1990, East Germany became part of the Federal Republic of Germany and the alliance, and in November 1990, the alliance signed the Treaty on Conventional Armed Forces in Europe (CFE) in Paris with the Soviet Union. It mandated specific military reductions across the continent, which continued after the collapse of the Warsaw Pact in February 1991 and the dissolution of the Soviet Union that December, which removed the de facto main adversaries of NATO. This began a draw-down of military spending and equipment in Europe. The CFE treaty allowed signatories to remove 52,000 pieces of conventional armaments in the following sixteen years, and allowed military spending by NATO's European members to decline by 28 percent from 1990 to 2015. In 1990 assurances were given by several Western leaders to Mikhail Gorbachev that NATO would not expand further east, as revealed by memoranda of private conversations. However, the final text of the Treaty on the Final Settlement with Respect to Germany, signed later that year, contained no mention of the issue of eastward expansion.

In the 1990s, the organization extended its activities into political and humanitarian situations that had not formerly been NATO concerns. During the Breakup of Yugoslavia, the organization conducted its first military interventions in Bosnia from 1992 to 1995 and later Yugoslavia in 1999. These conflicts motivated a major post-Cold War military restructuring. NATO's military structure was cut back and reorganized, with new forces such as the Headquarters Allied Command Europe Rapid Reaction Corps established.

Politically, the organization sought better relations with the newly autonomous Central and Eastern European states, and diplomatic forums for regional cooperation between NATO and its neighbours were set up during this post-Cold War period, including the Partnership for Peace and the Mediterranean Dialogue initiative in 1994, the Euro-Atlantic Partnership Council in 1997, and the NATO–Russia Permanent Joint Council in 1998. At the 1999 Washington summit, Hungary, Poland, and the Czech Republic officially joined NATO, and the organization also issued new guidelines for membership with individualized "Membership Action Plans". These plans governed the addition of new alliance members: Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, and Slovenia in 2004, Albania and Croatia in 2009, Montenegro in 2017, and North Macedonia in 2020. The election of French President Nicolas Sarkozy in 2007 led to a major reform of France's military position, culminating with the return to full membership on 4 April 2009, which also included France rejoining the NATO Military Command Structure, while maintaining an independent nuclear deterrent.

Article 5 of the North Atlantic treaty, requiring member states to come to the aid of any member state subject to an armed attack, was invoked for the first and only time after the September 11 attacks, after which troops were deployed to Afghanistan under the NATO-led ISAF. The organization has operated a range of additional roles since then, including sending trainers to Iraq, assisting in counter-piracy operations, and in 2011 enforcing a no-fly zone over Libya in accordance with UN Security Council Resolution 1973.