The North Atlantic Treaty Organization, also called the North Atlantic Alliance, is an intergovernmental military alliance of 32 member states—30 European and 2 North American. Established in the aftermath of World War II, the organization implements 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 threat posed by the Soviet Union. The alliance remained in place after the dissolution of the Soviet Union and the Warsaw Pact, 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. The organization's strategic concepts include deterrence.