The North Atlantic Treaty Organization (NATO) is an intergovernmental military alliance between 32 member states—30 in Europe and two 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 and deterrence, whereby its independent members agree to defend each-other from attack by any outside party. This is enshrined in Article 5 of the treaty, which states that an armed attack against the territory of 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. NATO undertook its first military intervention in the Bosnian War (1992–1995); with a United Nations mandate, it enforced a no-fly zone and defended UN safe zones. NATO also intervened in the Kosovo War in 1999 by bombing Yugoslavia with the stated goal of ending the violence and repressive actions by the Milošević government. Article 5 was invoked for the first and only time by the United States after the September 11 attacks, leading to NATO involvement in the War in Afghanistan (2001–2014), as part of the International Security Assistance Force (ISAF). In 2011, NATO intervened in the Libyan civil war, with a UN mandate to enforce a no-fly zone and protect civilians. The alliance has since been involved in training Iraq's military and countering piracy. Wikipedia