The acronym NATO stands for the North Atlantic Treaty Organization. Established in 1949, NATO is a military alliance formed in response to the geopolitical tensions following World War II, primarily as a collective defense measure against the Soviet Union. The organization consists of member countries from North America and Europe, committed to mutual defense in the event of an attack against any member state. NATO's core principle is collective defense, as outlined in Article 5 of the North Atlantic Treaty, which states that an armed attack against one member is considered an attack against all.