The establishment of NATO (North Atlantic Treaty Organization) in the 20th century was significant as it marked a formal military alliance among North American and European nations, primarily aimed at collective defense against the Soviet threat. Formed in 1949, NATO solidified transatlantic ties and represented a commitment to mutual defense, deterring Soviet expansion during the Cold War. NATO's principles influenced international security policy and prompted the creation of various defense arrangements in other regions. The organization continues to play a critical role in global security matters, adapting to new challenges such as terrorism and cyber threats.