The event that led to the creation of NATO in 1949 was primarily the growing tensions and hostilities during the early Cold War, particularly following World War II. The formation of NATO (North Atlantic Treaty Organization) was a response to the perceived threat posed by the Soviet Union and its expansionist policies in Europe. The treaty, signed on April 4, 1949, established a military alliance among 12 founding nations, pledging mutual defense against aggression. NATO aimed to provide collective security and deter Soviet influence, ultimately shaping the military and political landscape of the Western world during the Cold War and beyond.