The world relies too much on the indefinite continuation of the post-1945 taboo on military use of nuclear weapons. It was never a secure bar to such use, but now official statements and academic writings indicate a perceptible weakening of it. If a nuclear weapon country used its weapons in anger, anywhere, even on a relatively small scale, it would signal that nuclear war was no longer a theoretical possibility, but a reality. That realization is likely to have far-reaching political and social consequences worldwide. Yet it is hard to find any examination of what these consequences may be.

I don’t mean studies on the effects of nuclear weapons, or of a nuclear Armageddon, of which there is no lack. Anyone can access web-based graphic displays to estimate the devastation of a nuclear bomb dropping on his or her city. I have never heard of anyone moving out of one of those cities out of fear of a nuclear attack, but if a real nuclear bomb dropped somewhere, even far off, people are likely to think about it differently.

Nuclear terrorism: The diversion. I also don’t mean studies on what might happen if terrorists—rather than a country—used a nuclear weapon. There are many such studies, as well. The world’s leaders have adopted countering terrorist use of nuclear weapons as the main subject of the heavily advertised international security summits. It makes for “successful” meetings because all countries are on the same side in dealing with nuclear terrorism—they are all against it.

Nuclear terrorism is a concern, but the disproportionate official and academic focus on it diverts attention from the much more serious, but also much more difficult, problems of restraining countries that have nuclear weapons and keeping others who have an interest in getting them from doing so—and then using them. Dealing with nuclear weapon states, and would-be nuclear weapon states, means confronting argument over the rights and wrongs of nuclear weapon possession and considering major policy changes, all of which world leaders stay clear of.

Nuclear weapon use by nations. When it comes to nuclear weapon use by a nation, the most likely candidates are the countries outside the Nuclear Non-Proliferation Treaty—India, Israel, North Korea, and Pakistan—all of which are involved in territorial disputes that have led to wars. Initial nuclear weapon use may or may not involve large civilian casualties; it could in fact take place on a battlefield, with few civilian casualties. The current operative assumption in nuclear circles is apparently that after such an event the world would basically go on as it is, albeit with suitable changes in nuclear strategy by the other owners of these weapons, and possibly increased efforts by yet others to get the weapons, too.

But I think the more powerful result would be a sea change in the thinking of people around the world. They may decide, for example, that they don’t want to be anywhere near a potential target. Governments may find it difficult to maintain control without repressive measures. There may be a premium on shelter space. There are already news stories about the super-rich outfitting themselves with extraordinarily secure underground facilities. It sounds overwrought, but then we may be too complacent.

In the wake of military use of nuclear weapons, and the prospect of further use, popular movements may force changes—possibly violent changes—in the way that the world is organized. What these changes might be is difficult to say. We do know that the “experts” tend to underestimate the broader societal consequences of new circumstances that fall outside conventional assumptions.

Take a recent example: the 2011 Fukushima nuclear plant accident. A technical expert could have projected that a large tsunami would disable the safety systems of the plant and cause a severe accident. But no one had predicted that after the accident Japan, in reaction to public outcry, would then shut its nuclear reactors, and that the governments of a number of other countries would decide to end their nuclear power programs altogether.

Or consider the 2008 world financial crash. Not only did the central bankers insist in advance that it could not happen, but they failed to understand its broader economic significance even when important banks started to fail.

And, of course, there is the 100-year-old example of World War I. Even after the Austrian archduke’s 1914 assassination, no one expected a long world war that would destroy four major empires.

In the same way, nuclear weapon use by one of the nuclear weapons countries could have worldwide societal consequences far beyond what anyone imagines today.

Weakening the taboo. What has changed to weaken the taboo against nuclear weapons use? For one thing, the horror of nuclear weapons has diminished in the public mind. I am old enough to remember having to jump under my desk during “atomic” bomb drills in high school. There is almost no one alive today—and likely no one in a position of influence—who has seen a nuclear explosion. We know that the experience made a deep impression on many of those who did, and convinced them in a visceral way of the need for caution. New generations of officials and academics treat nuclear weapons as abstract chess pieces. Of course, none of them wants nuclear war, but one senses a new interest in playing with the possibilities nuclear weapons offer for increasing a country’s influence, or protecting it against others with nuclear arms.

Academic journal papers talk of a new renaissance in nuclear security studies that examine the extent to which such weapons increase a state’s bargaining power and its prestige, all with a view to making use of—if not the bomb itself—at least the shadow cast by the bomb. Some of these political strategists write as if there are quantitative laws that govern the deterrent effect and influence of nuclear weapons, laws which need only be discovered to be applicable by national leaders to their advantage. This is, of course, dangerous nonsense, but it provides a useful academic validation for powerful officials and bureaucracies involved with the weapons who want them—and thus the possibility of nuclear war—to remain an important aspect of national policy.

And while indeed no one wants nuclear war, it would also be only human if there were moments when some of the nuclear weapons advocates yearned for a chance to test the results of their work in the real world. It is easy to rationalize the notion by suggesting that the results would not be as bad as people think with small, modern nuclear weapons; that at the lower end of weapon yields, nuclear weapons overlap with conventional ones; that escalation can be controlled; and so on. We have been there before. In an early book, Henry Kissinger wrote: “With proper tactics, nuclear war need not be as destructive as it appears when we think of it in terms of traditional warfare.”

There is now also public discussion of the possible acquisition of nuclear weapons in countries where such public discussions never took place before, namely South Korea and Japan. They are obviously concerned about the failure of the major guardians of the Nuclear Non-Proliferation Treaty (NPT) to cope adequately with North Korea. While any step in the direction of nuclear weapons is still only a remote possibility in South Korea and Japan, it is no longer an unthinkable one. If either country did acquire nuclear weapons, it would surely be the end of the NPT. And while acquisition of nuclear weapons does not translate to use, the more countries with nuclear weapons, the greater the chances that things could go wrong.

Will deterrence prevent nuclear use? What could go wrong? Nowadays, respectable people in nuclear weapons countries insist that their weapons are not for use in fighting wars but purely for deterrence.

But what is deterrence? It is convincing opponents not to harm you out of fear that, if they do, you will harm them more than they can stand. You don’t have to think very hard to realize that nuclear deterrence is based on the threat to use nuclear weapons in certain circumstances (which for some countries include conventional attacks by their adversaries). In other words, deterrence cannot be divorced from use. That is why trained and dedicated officers in nine countries operate in shifts, waiting for orders to release their weapons. In other words, non-use is predicated on adversaries never using their nuclear weapons, or crossing some stated “red line.” One has the feeling that in the strategy of some countries, a so-called second strike may precede an adversary’s first strike.

One might ask, why in these circumstances would any country do anything that would risk nuclear retaliation? The short answer is that human beings sometimes do foolish things. Or they might evaluate the situation differently from their opponent, perhaps regarding the threat of a nuclear attack as a bluff.

To take a current example: If I understand correctly, Pakistan threatens to respond to an Indian military incursion with newly developed battlefield nuclear weapons. India previously threatened such incursions in response to what it claimed were Pakistani-sponsored terrorist attacks. Will India now be deterred from responding? Will Pakistan now refrain from supporting activities that may trigger an Indian response? Probably they themselves are not sure.

In one of his early books, Henry Kissinger described deterrence as a product of three multiplicative factors: “power, the will to use it, and the assessment of these by the potential aggressor.” (One always assumes nowadays that one’s adversary is the aggressor.) Two of the three factors are psychological. In other words, deterrence is in the mind of the adversary, and we know that minds do strange things. I would add another psychological element—the adversary’s evaluation of the consequences of not taking actions despite the risk of nuclear retaliation. It may be as simple as a politician knowing if he does not take the risk, he is finished.

Dangerous bias toward “hawks.” The risk of nuclear use is exacerbated by the cult of toughness at high levels in government. In a crisis, national leaders—likely tired, possibly awake with stimulants, and largely unfamiliar with the details, and perhaps even the basic facts, of nuclear weapon use—will be subject to multiple pressures, each with inevitable consequences for their political future. (That is, if the national leader is actually the one making the decision.) There is in these situations a bias in favor of hawks as opposed to doves. It is an age-old problem. In his history of the Greek wars, Thucydides famously commented that in times of war reckless audacity was equated with courage, and prudent hesitation with cowardice.

The experts describe the stability of deterrence as a delicate matter—with too little retaliatory power you risk attack, but if you threaten to build up too much strength, especially on the defensive side, the opponent may misinterpret it as initial steps toward aggression and you may risk preemptive attack. But if deterrence is a delicate affair that requires constant tuning by experts, is it something to count on never to fail?

That no nuclear weapons were used during the Cold War, and since, has been taken by the nuclear weapon professionals as a demonstration of the effectiveness of deterrence. But is this really a valid conclusion? For one thing, we know there were close brushes with possible use. For another, the lack of use does not necessarily translate into effective deterrence. There may be no deterrence at work at all if countries, even hostile adversaries, have no intention of using nuclear weapons against each other for reasons unrelated to the fear of retaliatory attack. What conclusions can be drawn from the decades of non-use of nuclear weapons for the future? None we can be sure of.

Accidental war. The taboo on nuclear weapons may also fail accidentally. There have been situations in both the United States and the Soviet Union/Russia that could have led to the launch of nuclear weapons by mistake but for the action of an individual officer. It would be surprising if such situations have not also occurred in other nuclear weapon countries. There have also been occasions when nuclear bombs fell out of airplanes on routine patrol. In one such case, a multi-megaton bomb very nearly exploded—after impact, five of six electronic locks failed.

A nuclear weapons enterprise requires extraordinary care and discipline at all stages, and never more so in dealing with weapons ready to launch. It is, however, extremely difficult to maintain proper discipline and motivation in a system that is never used. There are exercises and inspections, but that is not the same thing. There is a tendency, of which there is some evidence, to become sloppy. The nuclear risks are obvious.

Where now? There was a large element of luck in getting through the Cold War without nuclear weapon use. Will that luck hold?

The United States and Russia have reduced their large nuclear arsenals, but no other countries seem inclined to follow their lead. By all accounts, most other countries with nuclear weapons are building more, or modernizing them, or both. The countries outside the Non-Proliferation Treaty—India, Israel, North Korea, and Pakistan—are increasing the sophistication of their forces. India seeks a submarine-based strategic force, Israel already has one and is expanding it, North Korea is building more weapons and is experimenting with submarine-launched missiles, and Pakistan is introducing short-range nuclear weapons to counter a possible Indian conventional attack. It is difficult to believe that with all this expensive nuclear weaponry deployed, that the world's nuclear countries will confine its use to gaming nuclear exchanges and calculating whose weapons cast the larger and more ominous shadow.

As if to underline that we should expect no change in this picture, on October 27 the nuclear weapon countries (with the bizarre exception of North Korea) would not support a UN General Assembly resolution to start discussions on eliminating nuclear weapons. The resolution passed overwhelmingly and the negotiations will apparently start next year, with or without the nuclear powers. A hard look at the worldwide societal consequences of nuclear weapon use could help to support these discussions and underline their importance.

In the 1959 movie, On the Beach, a survivor of nuclear war asks, “If everyone was so smart, why didn’t they see this coming?” Exactly. Stop and think about what may be coming if we don’t act.

Above all, when it comes to nuclear weapons, we should not allow ourselves to just drift into the future. We need to look ahead as best we can and steer in a safer direction.