April 16 (UPI) -- NATO, created in 1949, has been the most successful alliance in history because member states of the Atlantic Community recognized that collective defense was essential to protecting security and preventing a catastrophe that followed World War I. The overriding threat was the Soviet Union until it imploded in 1991. Still, during the first four decades of its life, NATO was often at one crossroads or another. The Korean War, Dienbienphu, Suez, Vietnam, nuclear disarmament,