To counterbalance the threat of communism during the Cold War, NATO (North Atlantic Treaty Organization) was formed in 1949. This military alliance, comprising North American and European countries, was established to ensure collective defense against potential Soviet aggression. The key principle of NATO is mutual defense, meaning that an armed attack against one member is considered an attack against all. NATO not only served as a deterrent against the expansion of communism but also played a crucial role in the geopolitical landscape of the 20th century, particularly during the Cold War.