The Rest of the Nuclear Club

"''Luxembourg is next to go And (who knows?) maybe Monaco."

- Tom Lehrer, "Who's Next"

The US, Russia, the UK, France, and China all have nuclear weapons and get to deal with all the attendant politics thereof. Since their development, nuclear weapons have been used in warfare by one nation only two times: the United States against Japan in the 1945 bombings of Hiroshima on August 6, and Nagasaki on August 9. The sheer destructive effectiveness of these weapons shocked the entire world, including the US, and since then the only nuclear detonations have been tests or demonstrations.

In theory, only the Permanent Five (P5) members of the United Nations Security Council--i.e. the US, Russia, the UK, France, and China--are even allowed to have nuclear weapons, per the terms of the Non-Proliferation Treaty (NPT). That said, international law being what it is--i.e., highly voluntary--several states currently have, previously had, or may have or be developing nuclear weapons. For the most part, the non-P5 states that have/had nuclear weapons either did not sign the Treaty in the first place (India, Pakistan, Israel, South Africa) or withdrew from it (North Korea). The states that are suspected of developing weapons are generally parties to the NPT, and the shadiness about them is caused by their attempts to circumvent the controls they agreed to under the terms of the NPT.

Israel
Israel has nukes. Unofficially.

Israel being a nuclear power is frequently referred to as "the worst kept secret in nuclear politics". While the Israeli government refuses to officially admit that they have nuclear weapons, multiple leaks have confirmed to anyone interested that hell yes, they do. These leaks come from... the Israeli government (the arsenal's primary purpose is after all to intimidate the other side not to attack--secret doomsday devices aren't too good at that). That includes the Prime Minister (Ehud Olmert having once let slip in a speech that Israel has the Bomb before hastily retracting his statement). Basically, Israel wants you to know they've got the bomb. They just don't want to deal with the politics of being a nuclear power. While Israel refuses to comment on its nuclear capability (using the vague statement that they will not the first to "introduce" nuclear weapons), 80-400 warheads is the estimate, deployable via Jericho ballistic missiles, submarine based cruise missiles, and a wide range of fighter aircrafts, giving Israel a full nuclear triad.
 * Israel's nuclear ambiguity serves a much more complex purpose then simply being a way to avoid it having to "deal with the politics of being a nuclear power". Israel's suspected nuclear arsenal serves as both a deterrent against those who wish to attack it, and as a convenient justification to those who don't want to, but who need an excuse for avoiding it. It also serves as a way to ensure that no one would consider using weapons of mass destruction against Israeli citizens, for fear of the retaliation that would follow (Saddam use chemical weapons in the past against Iran and the Kurds, but never used them against Israel during Desert Storm). Meanwhile, by not going public with its being a nuclear power, Israel prevents a nuclear arms race, as most of the other Middle Eastern states don't feel a pressing requirement to acquire nuclear weapons. Thus, allowing the Middle East to remain a non-nuclear area on paper. It's taken as read that should Israel ever go public with its nuclear arsenal, the rest of the Arab world would withdraw from the NPT agreement and seek nuclear weapons themselves (the Middle East is just funny like that).

India
Detonated its first nuke in 1974 in what was termed a "peaceful nuclear explosion" entitled "Smiling Buddha" (one wonders if the actual Buddha would smile, but it's funny anyway; the name comes from the fact that the test happened to fall on a holiday marking the Buddha's birthday). Interesting because it's the first nuclear explosion to be ordered by a woman; Indira Gandhi was Prime Minister at the time. The main weapons are the Agni medium-range ballistic missiles, with an ICBM in development. The Su-30MKI "Flanker" is being adapted for nuclear use and its first missile sub has just been launched.

Pakistan
Pakistan tested its first nukes in 1998, developing them in response to India's test, although it is believed to have had them for many years previously. The country has an unknown number of nuclear weapons, but current estimates put it ahead of India in both weapons and delivery systems. Unlike India it has successfully developed a triad of systems which can be launched from land (Medium and Intermediate-range missiles) Aircraft and submarines, making this a much more sophisticated arsenal then the Indians; although this is at the cost of accepting Indian superiority in conventional weapons (the earlier doctrine called for approximate parity). Are currently making a nuclear submarine..

North Korea
The country conducted multiple nuclear tests, but these tests were underground and produced mediocre results. While it does not appear to have any actually practical weapons, despite the Kim regime's claims, it does appear to nominally possess nuclear arms.

Has conducted a good number of missile tests, including an indigenous ICBM, which has had two tests. This ICBM looks like it may be using the old Soviet R-27/SS-N-6 as its second stage (with some bought in the 1990s). Most of a nuclear capability, though, would be based on the large variety of "Scud" derivatives the DPRK has built.

With the ascendancy of Kin Jong-un, there has made allusions to North Korea being seriously considering ending its experiments, in exchange for badly needed donations of food and infrastructure. While an agreement was signed between North Korea and the USA in 2018 to close a research facility - intelligence reports claim the facility was no longer usable and North Korea continues to flaunt its (currently unsuccessful) ICBM program.

South Africa
During The Apartheid Era South Africa developed a small number of nuclear weapons, probably no more than 10. The very isolation that drove them to develop the weapons also limited their means of delivery, the ageing English Electric Canberra. In 1979 an American satellite detected what may have been South African nuclear test. Rumours of collaboration with Israel's nuclear program abound, but have never been proven. All weapons were dismantled shortly before the end of apartheid and South Africa helped establish the African nuclear-weapon-free zone.

Ukraine, Belarus and Kazakhstan
Between them inherited thousands of Soviet nuclear weapons after the fall of the USSR. They were all sent to Russia, and Kazakhstan has since became part of the Central Asian Nuclear-Weapons-Free-Zone.

Several Neorealist international-relations scholars--most notably John Mearsheimer--have advocated rearming Ukraine as a deterrent to war in Europe. However, given that their analyses were made in the late '80s and early '90s and assumed that the reunited Germany would be tempted to flex its muscles militarily, this theory is not given much credence these days. (As it turns out, the Germans hate war viscerally, and prefer to flex their muscles economically.) Also, that whole mess in Crimea in the mid-2010s and the follow-up in Donbass in the early-2020s showed that, if Ukraine had nukes, they might be tempted to use them.

Iran
The very big maybe. Though much of the world (including the International Atomic Energy Agency) is inclined to put Iran in the "trying to get" category, Iran's government maintains that it is only pursuing peaceful nuclear energy. The country's Supreme Leader Ayatollah Khamene'i issued a fatwa (Islamic judicial opinion) condemning nukes, but Khamene'i isn't the most trustworthy man around by a long shot. The Iranian government may or may not be distanced from the populace, as there exist large numbers of pro- and anti-government Iranians.

The United States helped start Iran's nuclear program in the 1950s as part of the Atoms For Peace program.

Has recently conducted tests of medium-range missiles, with the range to hit Cyprus and Bulgaria. Could be collaborating with North Korea to build missiles.

Syria
Suspected to be developing nuclear weapons by many. Israel destroyed a suspected nuclear reactor in an airstrike in 2007.

Taiwan
Refuses to confirm or deny rumors, but it has six operational nuclear reactors (for power generation, sure, but it's trivially easy to convert one into creating weapons-grade nuclear fuel) with two more in construction; additionally, back when the United States still had official diplomatic relations with Taiwan a lot of advanced physicists were sent there for an unspecified reason and there was that one time during George W. Bush's presidency that a ship full of warheads and other stuff got "accidentally" shipped to Taiwan...
 * It is most certainly not "trivially easy" to convert a nuclear power plant into a facility that would create weapons-grade nuclear fuel. The amount of plutonium-239 (the main ingredient in weapons-grade nuclear material) produced by a nuclear power plant is trivially small compared to the cost and effort that would be required to separate it from all the plutonium-240 that it it also produces. Fuel for a nuclear power plant contains 18%+ of Pu-240, whereas weapons-grade material contains <7%. You need a special type of reactor to specifically produce Pu-239. Basically, it's actually less of a pain in the butt to just build a reactor specifically to create Pu-239 than it is to try to separate it out from spent nuclear fuel rods.
 * To wit, Taiwan's nuclear reactors are either boiling water reactors (BWR) or pressurized water reactors (PWR), both of which are light water reactors. In contrast to heavy water reactors (which use deuterium oxide rather than "regular" water), light water reactors do not produce nearly as much plutonium or thorium waste, and require pre-enriched rather than standard uranium as fuel, which is more strictly regulated than the stuff you can just dig up and refine. If they were secretly attempting to build a nuclear arms program, they would have either argued the fuel standpoint in order to adopt the use of at least one heavy water reactor in the first place like India or Pakistan. It's just impractical to do it otherwise.

Argentina
Developed a short lived, secret program during its military dictatorship, but it never got very far and all such work stopped completely when civilian government took power again. This was probably, in part, due to its rivalry with Brazil.

Brazil
Virtually the same as Argentina, including the rivalry part. The military dictatorship pursued a nuclear weapons program covertly, but never got very far and since the restoration of democracy, the program has been completely disbanded. Note: the Brazilian government is very touchy about its refinement technology, leading to a bit of a spate with the IAEA monitoring a plant, but this isn't because anyone seriously suspects of an illegal program; it's just that the government (rightly or wrongly) believed that inspections would be tantamount to industrial spying on their secret centrifugal axis technology, based on electromagnetism. And it was all sorted out in the end, to everyone's satisfaction.

Egypt
Egypt flirted with nuclear weapons in The Sixties (Tom Lehrer wasn't entirely joking), but the project was always halfhearted and was completely abandoned by 1980. Egypt does have a peaceful civilian nuclear program, which has been gathering steam of late and has drawn some extra attention after the Revolution of 2011, but as long as Israel doesn't officially declare its weapons, Egypt will almost certainly make no attempt to weaponize its program.

Germany
During World War II, the Third Reich commissioned a heavy water production scheme for potential nuclear weapons use. That is, until the Norwegian resistance movement successfully sabotaged it in 1943. Even without the sabotage, the Third Reich would still have been a long way off producing any warheads.

Japan
Similar to Germany, Imperial Japan during World War II attempted to develop a nuclear weapon. Also similar to Germany, the program was pretty much doomed from the start, and didn't get very far. Today, Japan does theoretically have the resources to produce nuclear weapons (see below) in a matter of months given its resources and status as an economic juggernaut, but they've never pursued the idea for two reasons. One, they're under the protection of the most powerful military in the world already. Two, as the only country ever to have nuclear weapons used against them, the idea of a nuclear weapons program is widely viewed as taboo.

Iraq
In the 1980's, the Iraqis did have a nuclear program which went through two phases. The first 'phase' began some time in the 1970s was based around the Osirak Reactor. When the Israeli's bombed that to piece the Iraqis, were forced to revamp the project. From here, the second phase was a somewhat more distributed project based around uranium enrichment. Then the Gulf War happened and the program was utterly demolished by American air strikes. After that war, the program never amounted to anything more then, in the words of one military analyst, "a bunch of papers buried in a physicist's backyard."

Sweden
Despite the country not having been at war since 1814, Sweden started a covert nuclear weapons program after WWII that was only abandonded in 1972 (in favor of development of the Saab 37 Viggen). The reasoning behind Sweden's program was maintenance of its neutrality: since Sweden declined to join NATO, it could not expect to fall under the American military and nuclear umbrella. A Swedish Bomb would have probably been an effective deterrent to the Soviet Union trying to involve Stockholm in the Cold War.

Yugoslavia
Yugoslavia started a nuclear weapons program in The Fifties, but abandoned it after the thawing of Soviet-Yugoslav relations in The Sixties, and became a firm proponent of non-proliferation. However, after India detonated its first bomb (see above), the program was revived. The program was again abandoned in 1987 due to the country's financial troubles, impending breakup, and the Chernobyl disaster.

Nuclear sharing
Several non-nuclear members of NATO participate in nuclear weapons sharing with the US: in the event of World War III, some or all of the American bombs stationed in their territory would be turned over to the their governments to dispose of as they deemed necessary. Germany, Belgium, the Netherlands, Italy, and Turkey participate in the program, while Canada and Greece used to participate but have since withdrawn from the program (Canada in 1984, Greece in 2001).

Nuclear breakout capacity
This is a technical term referring to the ability to quickly build a nuclear weapon: it generally means that the country in question has all of the know-how needed to build a weapon and most if not all of the infrastructure, but have not for whatever reason actually built a weapon.

Fortunately or unfortunately building a bomb is not easy and is in fact, literally rocket science. Experience has shown that a country needs


 * Technical know how. How to convert the theoretical knowledge into a working programme.. It is quite difficult to obtain that without rousing suspicion.


 * A large industrial base. A nuclear weapons programme cover so many fields that just setting up a reactor is not enough, you need hundreds of process to convert that weapons material into a deliverable device. If your domestic industry cannot manufacture them, well you are out of luck. The Manhattan project had to develop an industrial infrastructure larger than the Car industry.


 * Money..............lots of it. The Manhattan project cost more than the Space programme did.

These three are the inherent limiters. How they effected our current powers.


 * Of the nuclear club, the P-5 already had them and that was that.


 * Israel lucked out that they got information from Jewish Scientists who had worked on the Manhattan project (many of whom remember had escaped Hitler's Germany and then Europe).


 * Both India and Pakistan had scientists who had worked on the Manhattan Project (see a pattern?)as part of British India, and also the later British effort to develop an Independent nuclear deterrent. The both had by the 1970's the Industrial base and the monies to fund it.

So how does that leave the aspiring/failed powers?


 * North Korea c;early has deficiencies in all three areas, which would explain their failed tests. It is heartening to know (after a fashion) that even where a nation state has put all of its resources into it, success is not guaranteed. However, the North Koreans could possibly succeed still.


 * Iran has number three; the funds. They possibly have the Industrial Infrastructure, though the jury is still out on that. It is in the technical know how most people feel that it will be decided.

For those who have the basis, depending on how you define it, breakout capability could refer to anything from "could build a bomb in six months" to "could build a bomb in six months once they built the infrastructure, which would take at most a year or two more." Japan, Germany, Sweden, Canada, and the Netherlands all have the infrastructure in place (although Germany is seriously considering dismantling it, and Japan would of course have to be in really dire straits before it even thought about building a bomb), while Brazil, Argentina, Taiwan, and Australia would need a few years to build up the infrastructure and collect enough U-235 or plutonium and they probably lack the know how, something which they could (probably) rectify. Saudi Arabia barely has the infrastructure or know how at all, but with its money, it could possibly buy its way into the breakout-capacity club.

Breakout capacity has come to the fore in recent years on account of the aforementioned Iran thing. The most important one is probably the positions of the US and Israel on the right moment to attack Iran: while the US has frequently reiterated that it would be willing to make a military strike if Iran developed a nuclear weapon (i.e. built the damn thing), Israel has just as frequently reiterated that it is unwilling to let Iran get into a situation where it had the ability to develop a nuclear weapon (i.e. developed breakout capacity).