The North Atlantic Treaty Organization (NATO NAY-toh; French: Organisation du traité de l'Atlantique Nord, OTAN), also called the North Atlantic Alliance, is an intergovernmental military alliance between 32 member states—30 in Europe and 2 in North America. Founded in the aftermath of World War II, NATO was established with the signing of the North Atlantic Treaty in 1949. The organization serves as a system of collective security, whereby its independent member states agree to mutual defence in response to an attack by any outside party. This is enshrined in Article 5 of the treaty, which states that an armed attack against one member shall be considered an attack against them all.
Throughout the Cold War, NATO's primary purpose was to deter and counter the threat posed by the Soviet Union and its satellite states, which formed the rival Warsaw Pact in 1955. Following the dissolution of the Soviet Union in 1991, the alliance adapted, conducting its first major military interventions in Bosnia and Herzegovina (1992–1995) and Yugoslavia (1999). Article 5 was invoked for the first and only time after the September 11 attacks, leading to the deployment of NATO troops to Afghanistan as part of the International Security Assistance Force (ISAF). The alliance has since been involved in a range of roles, including training in Iraq, intervention in Libya in 2011, and countering piracy.
Since the end of the Cold War, the alliance has accepted sixteen new members, incorporating former Warsaw Pact countries and post-Soviet states. NATO and Russia have co-operated, but Russian leaders have called this eastward enlargement a threat to its security interests, and oppose Ukraine joining NATO. The Russian annexation of Crimea in 2014 prompted strong condemnation from NATO and a renewed focus on collective defence.
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