Today, there are only 9 countries with nuclear weapons. These are-

USA
France
UK
Russia
China
India
Pakistan
North Korea
Israel
Let us first see why these countries established a nuclear arsenal.

Well, the first country to have nukes was USA. They used it to end World War 2.

They soon realized that nuclear weapons was something that gave one’s country tremendous power and influence.

Also, WW2 was the starting of the Cold War.

The Soviet Union wanted nuclear weapons as well to be in competition with USA. So, they developed the most powerful bomb ever- The Tsar bomba. This was 3800 times more powerful than the Hiroshima nuclear bomb.

Soon, after the collapse of the Soviet Union all its nuclear weapons went to Russia. In fact even though countries like Ukraine and Kazakhstan had nuclear weapons they gave them to Russia and in return Russia signed an agreement to never violate their territory in the future.

France and Britain also started to accumulate nuclear weapons after they won World War 2.

Around the 1970’s countries like India and Pakistan developed nuclear arsenals due to tensions between them. Proliferation continued through the 1980’s and especially in the 1990’s.

Meanwhile China got started on its own nuclear weapons due to the aggression it faced from the West. At this time India and Russia were stronger allies and Pakistan was more of a mediator. Now things have changed.

(I hope you’re starting to see a trend here)

Around the start of this millennia North Korea also started to accumulate a nuclear arsenal. Now it’s mostly just for the heck of it so they are mostly an exception. They have fewer than 10 warheads which don’t really provide as much security.

At the time, the Nuclear Non-Proliferation treaty was being signed. South Africa was the only country which decided to dismantle its nuclear arsenal because it wanted peace.

There were rumors that Iran intended to make nukes, however recently the JCPOA was signed which prohibits Iran from making nukes for the next 15 years.

Israel also has nukes. They are expected to range in between 100- 500 for most rough estimates, however, there has never been an official report. They have neither denied nor confirmed the existence of their nukes. It’s a sort of the thing where nobody really talks about it but everybody knows they have it. However, the primary purpose behind their arsenals is to deter countries they face aggression from (like Iran).

Now we see that all countries who have nukes today got them for the same reason- they all faced aggression or a threat from a hostile nation.

In fact all countries who maintain their arsenals today, also maintain it for the same reason- Mutually Assured Destruction.

It is a doctrine of military strategy and national security policy in which a full-scale use of nuclear weapons by two or more opposing sides would cause the complete annihilation of both the attacker and the defender. It is based on the theory of deterrence, which holds that the threat of using strong weapons against the enemy prevents the enemy's use of those same weapons.

More importantly, the strength of one’s nuclear arsenal matters.

USA has around 7000 nuclear weapons. 7000 nukes is enough to destroy just about any country completely (say Russia). For this reason Russia wouldn’t want to attack USA as they know it would mean a suicide mission.

On the other hand, China has about 300 nuclear weapons. This is enough for them as they don’t face an imminent military threat from any country (like USA or Russia).

It is not important for just any country to have a nuclear arsenal. Most don’t need it or can’t afford it.

However, it is vital for a country to have a nuclear arsenal if its adversaries do.

Hence, that’s by far the biggest reason most countries don’t accumulate a nuclear arsenal- they don’t need it.

Most are protected by bigger, more powerful allies and others don’t really have any enemies.

Apart from this, there is obviously the fact that not all countries can afford nuclear weapons in the first place which has been pointed out quite well by the rest of the answers.

Yet there are still more reasons countries refrain from getting nuclear weapons.

One of these is international agreements. The NPT is a great example of this. Countries get benefits for giving up their arsenals. The NPT has just about every country as a party and it forbids nuclear weapons.

Another reason is international pressures. International pressure works pretty well too. Countries can condemn other countries for doing illegal nuclear weapons tests. When this escalates, economic sanctions and embargoes are put on which pressures the country to give up its arsenal because of the economic instability it faces. North Korea is a good example of this.

Lastly, unilateral deals with other countries has been working well too. A good example of this is the Iran nuclear deal, where the P5+1 countries stopped Iran from getting a nuke and in return many sanctions and embargoes were removed which boosted Iran’s economy. Win-Win situation!

Hope that helps. I would love to know what you think about this.

Source: Quora.com

The reasoning of the poster above me get as e be ooo...

Why can't every household have air conditioning system?

Why can't every household have Mikano 10 KVA diesel generator?

NobleSeed:
no be only nucks na nudes..
Them tell you say na dillards dey produce nucks abi? Who won produce am by the way? Na who don chop belleful dey think of producing nucks . naija isn't ready not even in 1000yrs to come

9ja for that matter, bro that means we go just wipe out our civilization by ourselves.

We go come hear say Nuclear forces embarks on 3 months strike.

sinkhole:
Why can't every household have air conditioning system?

Why can't every household have Mikano 10 KVA diesel generator?

You have a point to a point.

That would bring relative peace on earth.

But then, some people don't want peace.