The North Atlantic Treaty Organization (NATO) 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.