The event in 1949 that marked the beginning of the nuclear arms race was the successful test of an atomic bomb by the Soviet Union. This followed the United States' development and use of atomic bombs in World War II, primarily in Hiroshima and Nagasaki. The Soviet test demonstrated their capability to produce nuclear weapons, instigating a competitive escalation in armaments between the two superpowers during the Cold War. This arms race led to the stockpiling of nuclear weapons and heightened tensions as each side sought to deter the other through the threat of mutual destruction. The implications of this event continue to influence global politics and discussions on nuclear disarmament today.