Give me a few key facts from the paragraph below

Context: The North Atlantic Treaty Organization, also called the North Atlantic Alliance, is an intergovernmental military alliance between 31 member states – 29 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.

Answer: The North Atlantic Treaty Organization (NATO) was established on April 4, 1949. As a military alliance, it serves as a unified defense organization for its member countries. For example, it served as a check against Russia during the Cold War. NATO has 31 member countries today.