Between the 1960s and the 1990s, people lived under the shadow of the fear of nuclear war:
The atomic bomb changed international relations. The superpowers, that is the USA and the Soviet Union, did not dare to start a war because both sides had nuclear weapons. There was a period of 'Cold War' where the two sides opposed each other without actually going to war themselves.
The dropping of the atomic bomb therefore holds major historical significance. It was an event which shaped history for many years and one which had lasting impacts. It not only sparked the advent of other weapons, it also influenced relations between countries and instilled a sense of fear around the world. It still does so today with the west worried about the nuclear capacity of nations like North Korea.