Nuclear weapons had played a vital role during the cold war. When the cold war had ended in late 1980s and the early 1990s, there was a sense of relief as a great threat to the world was over. However, right after that, the idea that the possession of nuclear weapons by some country might lead to the spread of nuclear technology in the world did worry people. People believed that this might lead to great destruction and harm to world if the usage became common, thus, making the world a dangerous place to live in. (Sir Laurence Martin)
Defense - Almost every nation in today's world is under threat by one or the other nation for various reasons, example; political, resources, history and religion. Every civilian needs the head of state to take responsibility of their security and to let peace prevail. State security requires a good military force and arsenal, so that if it is attacked by a rival state, they can fight back and protect their nation and people. Nuclear weapon is although dangerous, but it is a very strong type of weaponry which gives a sense of security that fighting back will not be a problem at all.
Prestige - In the post cold war world, only very strong nations such as the UK, USA, France, Russia and China possess nuclear weapons. Being a part of the nuclear block and becoming a nuclear power is a matter of pride, as you are then counted among the few dominant states of the world. For example, India and Pakistan wanted to join the nuclear club because they wanted to be declared as independent states that would stand up against their adversary without fear.
Deterrence - Simply any person ruling a state that does not possess nuclear power would think a million times before attacking a state that has nuclear power. Or if both rival states possess nuclear power, both would know that their opponent is equally potent, and if nuclear weapons are used to settle the dispute, the world will face major destruction. For example, India and Pakistan have been on hostile terms for a long time now and have also had many wars with other another; but ever since both of them became nuclear powers, they don't even consider attacking the other, as they know that they will be answered back with a nuclear attack too. Thus, it can be said, that nuclear power brings about 'Balance of Terror' in the world.
Disadvantages of Nuclear Power:
Hazardous - The abbreviations 'MAD' and 'WMD' are often attached to nuclear weapons, which stand for 'Mutually Assured Destruction' and 'Weapons of Mass Destruction' respectively. It is common knowledge that nuclear weapons are extremely destructible, so much that alone Russia's nuclear weapons can destroy the world three to four times. The incident of Hiroshima and Nagasaki is a very appropriate example to show the extent of annihilation that can be caused by nuclear weapons.
Compellent - If a nation's rival becomes a nuclear power, it is an evident threat for its rivals, as no nation can fight back nuclear weapons using conventional weapons. This compels one nation to another to take a step towards the possession of nuclear weapons. India became a nuclear power because it had antagonistic relations with China, which was a nuclear power. Following that, Pakistan became a nuclear