Established in the aftermath of World War II, the organization implements the North Atlantic Treaty, which was signed in Washington, D.C., on 4 April 1949. NATO is a system of collective security: 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.

NATO's main headquarters are located in Brussels, Belgium, while NATO's military headquarters are near Mons, Belgium. The alliance has targeted deployments of their NATO Response Force in Eastern Europe, and the combined militaries of all NATO members include around 3.5 million soldiers and personnel. Their combined military spending as of 2020 constituted over 57 percent of the global nominal total. Members have agreed that their aim is to reach or maintain the target defence spending of at least two percent of their GDP by 2024. Wikipedia