The North Atlantic Treaty Organization (NATO) is an intergovernmental military alliance comprising 31 member states, including 29 European and two North American nations. Originating after World War II, NATO enacted the North Atlantic Treaty on April 4, 1949, in Washington, D.C. It operates on a collective security system, with member states pledging to defend each other against external aggressors. NATO played a crucial role during the Cold War in countering the Soviet Union's threat and continued its operations post the Soviet Union's dissolution and the end of the Warsaw Pact. Headquartered in Brussels, Belgium, NATO has its main military headquarters close to Mons, Belgium. The alliance has bolstered its NATO Response Force deployments in Eastern Europe. The combined militaries of all NATO members consist of approximately 3.5 million soldiers and personnel. Their combined military spending, as of 2022, constitutes around 55 percent of the global nominal total. Member states have committed to maintaining a defense spending of at least two percent of their GDP by 2024. NATO started with twelve founding members and has expanded nine times, most recently with Finland joining on April 4, 2023, exactly 74 years after NATO's inception. Sweden's accession is anticipated, with its Accession Protocol to the North Atlantic Treaty being ratified. Additionally, NATO acknowledges Bosnia and Herzegovina, Georgia, and Ukraine as aspiring members. However, enlargement has caused tensions with non-member Russia, along with twenty other countries participating in NATO's Partnership for Peace program. Furthermore, nineteen countries engage in institutionalized dialogue programs with NATO.

NATO - Wikipedia