Everyone knows the the nine nations that already posses nuclear weapons, and the ability, to one extent or the other, deliver them: The U.S., Russia, Great Britain, France, China, Pakistan, India, Israel and North Korea.
Some of those countries have what has been called a triad defense, ie three ways of delivering nukes on target; via silo or mobile land-based launches, aircraft drops and guided missile sub launches. There's also evidence that nuclear missiles can be launched horizontally from submarine torpedo tubes. And of course there are the famous suitcase nukes, much beloved in fiction, but having some basis in actual fact.
Other countries rely only on fighter/bomber aircraft and a variety of mobile missile launchers.
But, and this is important, according to Laurence Martin in his book The Changing Face of Nuclear Warfare, which was published a number of years ago, at least eight other nations have the materials and the expertise to construct nuclear weapons. Among them, including some surprises, are Argentina, Brazil,Egypt, Iran, Libya, South Africa, South Korea and Taiwan.
What he means is that those nations posses uranium reserves, maintain research reactors which can produce the raw materials for weapons grade products, most of them operate power generating reactors also capable of producing material that could be re-processed into weapons grade products, and some have constructed enrichment, reprocessing and heavy-water plants, and have personnel trained at the very good to excellent level.
That's not to say any of those nations, other than Iran, are actually making efforts to produce nuclear weapons--but they have the means and the capability to do so. If the will is there, the world's nuclear club could double in size.
What should we do about it? What can we do? Maybe Kirk McGarvey knows.