Given North Korea's nuclear lunacy, what exactly are the rules, formal or implicit, about which nations can have nuclear weapons and which cannot?
It is complicated.
In the free-for-all environment of the 1940s and 1950s, the original nuclear club included only those countries with the technological know-how, size and money to build nukes. Those realities meant that up until the early 1960s, only Britain, France, the Soviet Union and the United States had nuclear capabilities.
Members of this small club did not worry that many other nations would make such weapons because it seemed far too expensive and difficult for most.
During the Cold War, the Soviet Union and the United States adhered to an unspoken rule that their losing Axis enemies of World War II -- Germany, Italy and Japan -- should not have nuclear weapons. Despite their financial and scientific ability to obtain them, all three former Axis powers had too much recent historical baggage to be allowed weapons of mass destruction. That tacit agreement apparently still remains.
The Soviet Union and the United States also informally agreed during the Cold War that their own dependent allies who had the ability to go nuclear -- including Eastern Bloc nations, most Western European countries, Australia and Canada -- would not. Instead, they would depend on their superpower patrons for nuclear deterrence.
By the 1970s, realities had changed again. Large and/or scientifically sophisticated nations such as China (1964), Israel (1967) and India (1974) went nuclear. Often, such countries did so with the help of pro-Western or pro-Soviet patrons and sponsors. The rest of the world apparently shrugged, believing it was inevitable that such nations would obtain nuclear weapons.
The next round of expansion of the nuclear club, however, was far sloppier and more dangerous. Proliferation hinged on whether poorer and more unstable nations could get away enriching uranium or acquiring plutonium in secret.
Some nations let on that they were developing nuclear weapons and were stopped by preemptive military strikes, such as Iraq and Syria. Others, including South Africa, Ukraine and Libya, were persuaded to halt their nuclear projects.
Pakistan was the rare rogue that managed to hide its nuclear enrichment, shocking the world by testing a bomb in 1998. Pakistan rightly assumed that once a nation proves its nuclear capability, it is deemed too dangerous to walk it back through disarmament.
Nonetheless, until the official nuclearization of North Korea in 2006, the nuclear club remained small (eight nations) and was thought to be manageable. Why?
First, those nuclear countries that were relatively transparent and democratic (Britain, France, India, Israel and the United States) were deemed unlikely to start a nuclear war.
Second, the advanced but autocratic nuclear nations (China and Russia) were thought to have too much at stake in globalized trade and national prosperity ever to start a lose/lose nuclear war.
Third, any unstable rogue nuclear nation (Pakistan) was assumed to be deterred and held in check by a nearby nuclear rival (India).
The nuclear capability of dictatorial North Korea (and likely soon, theocratic Iran) poses novel dangers far beyond the simple arithmetic of "the more nuclear nations, the more likely a nuclear war."
Neither North Korea nor Iran is democratic. Neither is a stable country.
Neither has an immediate nuclear rival that can deter and persuade it not to dare use a nuclear weapon. Both started nuclear programs in secret. Both hate the United States and its allies.
More importantly, their flagrant violations of nonproliferation accords and their perceived aggressiveness will prompt relatively powerful regional neighbors such as Egypt, Japan, Saudi Arabia, South Korea and Taiwan to consider developing nuclear capability.
The club then could get big quickly.
Not all of these would-be nuclear powers are democratic. But they do share a single pro-American outlook.
A frustrated America may feel that China and Russia have encouraged rogue countries such as Iran and North Korea to develop nuclear weapons programs, selfishly assuming that missiles in those countries would be pointed at the West and not eastward. So now the United States is in a paradoxical position. It wants to stop all nuclear proliferation. But America also assumes that the next nuclear powers (for a change) would be pro-American -- a payback of sorts to China and Russia for allowing their rogue friends to develop nuclear capabilities.
The United Nations and international nonproliferation organizations, while well-meaning in intent, have thus far proven impotent in deed.
Yet amid the chaos, until 2006 there were implied rules for the eight-member nuclear club. Now, after North Korea's unhinged threats, those shared assumptions about nuclear poker are null and void. And no one quite knows what to expect next.