Nuclear weapon threat :
We can never be sure, that a nuclear attack by a superpower against a smaller country cannot be carried out. Sometimes, smaller nuclear powers like India and Pakistan may be the cause of tension. Small attacks may even be directed towards cities. There may be use of air-burst or ground-burst, with bombs in the ten- to one-hundred kiloton range. A terrorist type of attack is the most likely risk, and might be done for blackmail or ransom, or might be directed by an unidentified power against a superpower. Weapons may be acquired from the rival superpowers. Or, there might be an accidental launch of missiles.
Cold War :
The state of international stand-off after the second world war is called as the 'Cold war'. Though, there could have been another world war, the superpowers were well aware that it would annihilate the human race as nuclear weapons would naturally be used.
The first atomic bombs were by the Allies in World War II to destroy places of strategic importance. In the cold war, the US did use bombers against the USSR. Later, the USSR built its own nuclear weapons. The US and USSR used massive retaliation as one of the policies. The nuclear age and these wars opened a wide array of opportunities for physicists who proposed new theories which were deployed by these superpowers in every way to weaken each other through nuclear weapon projects. The cold war further led to conflicts like the Korean war and the Arab-Jew conflict. Moreover, smaller countries started building their own nuclear weapons insisting threat of local rivals. India, Pakistan and China are good examples of this. The CTBT which would have been a step ahead in reducing the nuclear weapon threat failed as powers like India and Pakistan have not signed it. These powers recently conducted nuclear tests due to which the world imposed economic sanctions on them. The exchange of nuclear weapons and even economic aid between the small players and superpowers has certainly led to a diplomatic game - The conditions that led to the two world wars. The UN has not succeeded fully in controlling the nuclear weapon race.
Conclusion :
The threat of an impending nuclear war can never be denied. This threat can be reduced to some extent through peace programmes by various organistaions and convincing the world about the dreaded effects of nuclear warfare and weapons. If World War - III occurs and nuclear weapons are used, the Human race would be annihilated and victory would not be a pleasure for anyone.
See Also :
Harry Truman
Winston Churchill
Joseph Stalin