Dividing historical periods into eras is often a difficult endeavor, if only because contemporaries rarely recognize the age they live in as new or special.

The First Nuclear Age

Few would have anticipated in 1945 that the bombings of Hiroshima and Nagasaki would herald the beginning of the ascent of nuclear weapons as a central currency of power in the East-West conflict. Instead, U.S. military leaders tended to consider nuclear weapons as a sort of heavily reinforced artillery that helped them "get more bang for their buck." It was only during the Cuban Missile Crisis in 1962 that officials in Washington and Moscow realized that nuclear weapons could well bring about the end of the world. The logic of nuclear deterrence began to take shape: there was no gain—however large—an aggressor could hope for that would compensate the immeasurable damage he would suffer from his enemy's nuclear retaliation. In a nuclear war, there could be no winners, only losers.

The arsenals of nuclear weapons on both sides thus gained the power to exert, through mutual deterrence, a moderating influence on political decisions in the East and in the West. They altered the cost-benefit calculation of a potential aggressor by drastically demonstrating to him the dangers of his actions. Avoiding the use of nuclear weapons therefore became the stated aim of the two superpowers. At the same time, the use of nuclear weapons—and this is one of the fundamental dilemmas—had to be a very real possibility in order to achieve a credible political deterrent. This means that it must be possible to use nuclear weapons in order to prevent them from being used. This inherent contradiction in the concept of nuclear deterrence has always been difficult to explain to the public.

Mutually assured destruction did not only prevent a nuclear conflict, but also prevented a conventional war between the two blocs. Since any military confrontation would have carried the risk of escalating into an atomic exchange, there was an apparent reason to exercise restraint—whoever shoots first dies second. Instead, the adversaries fought proxy wars and attempted to win the arms race between their opposing systems. Whenever a crisis threatened to escalate into a nuclear conflict, caution was the order of the day. The absence of a Western response to the building of the Berlin Wall or to the Soviet invasion of Czechoslovakia are cases in point.

Some observers even believed that a "nuclear taboo" would increasingly establish itself in East-West relations. The longer nuclear weapons were not used, the greater the aversion on both sides would be to ever cross the nuclear threshold and to open the nuclear Pandora’s box at all. It would therefore eventually become virtually impossible to use nuclear weapons. However, others dismissed such considerations as being excessively academic. They believed that in extreme crises, instead of continuing with long-standing patterns of behavior, decisionmakers were more likely to make decisions based on their own perceptions and immediate constraints.

The Second Nuclear Age

The fall of the Berlin Wall thus ended the First Nuclear Age, without a nuclear holocaust as was so often predicted. That the end of the Cold War would mark the immediate beginning of a new atomic era was not initially obvious. While nuclear weapons arsenals were significantly reduced, especially by the Western powers, traditional ways of thinking prevailed when it came to the function of the remaining arsenals. Nuclear weapons were considered to be insurance against a possible restoration of Soviet/Russian power. Very few experts thought about what the purpose of nuclear weapons might be in what was supposed to become a partnership with Russia.

The nuclear tests performed by India and Pakistan in 1998 provided a taste of what were to be the new challenges of the Second Nuclear Age. Two states had joined the nuclear club and posed no immediate threat to the United States or Russia, but targeted their nuclear weapons against each other. What is more, India saw its nuclear potential as a deterrent against China, while Beijing's concerns were directed at Moscow. Suddenly, deterrence had become multilateral instead of bilateral. How was a logic of deterrence to be formulated that would force India and Pakistan to exercise nuclear restraint in the event of a conflict? Would Moscow or Washington really be able to threaten Islamabad or New Delhi with nuclear annihilation should any of the two cross the nuclear threshold and use nuclear weapons against their neighbor?

The transition to a new age became even more apparent when, three years later, the September 11 attacks happened. Instead of hostile governments, suddenly violent Islamists were capable of committing mass murder and humiliating large military powers. Against such threats, nuclear weapons turned out to be virtually useless. Nonstate actors have no address to which one's nuclear deterrence threat may be directed. What is more, if the attackers are fanatics willing to sacrifice themselves, the traditional logic of nuclear deterrence will fail, since it is based on a mutual interest in survival.

Instead, another nuclear disaster was looming. Nuclear material in the hands of terrorists—whether in the form of nuclear weapons or as easy-to-build "dirty bombs" (mixing conventional explosives with radioactive substances)—seemed an ideal means of conducting high-profile attacks. If the idea of a "nuclear taboo" ever had a binding effect in the East-West context, it came crashing down with the twin towers in New York. In order to achieve their objective of spreading terror and fear, terrorists would be particularly keen to break this taboo, provided that they managed to obtain a nuclear explosive device.

The Second Nuclear Age was thus no longer only about deterrence between nuclear powers. It was also about recognizing and preventing possible terrorist attacks—whether nuclear or conventional. For this reason, intelligence agents became more important than the nuclear strategists of the Cold War. Strategies, called nuclear forensics, were developed that made it possible to determine the origin of fissile material used even if an explosion was induced by terrorists. Based on the radiation released, experts can read “nuclear DNA" like a fingerprint and match it to the country that produced the material. If it could then also be proven that the country of origin passed on the nuclear weapons material intentionally, for instance to provide targeted support for terrorist objectives or groups, the persons pulling the strings could be held accountable.

Given this complicated nuclear challenges, some people thought it was almost logical to completely abolish nuclear weapons in the future in order to eliminate the nuclear element from international politics once and for all. President Obama's dream of a world free of nuclear weapons, which he announced as a political objective in his speech in Prague in 2009, also reflected this stance. Obama's concept of "global zero" was met with a very positive response—at least in the Western world—and rewarded with the Nobel Peace Prize.

The Third Nuclear Age

Future historians will mark 2014 as the beginning of the Third Nuclear Age, linking this turning point to the illegal Russian annexation of Crimea. With this act, Russia finally left the pan-European security order, terminated its partnership with NATO and has (again) been using its enormous nuclear potential to threaten its neighbors ever since. By conducting flyovers with nuclear bomber aircraft and simulating nuclear strikes against Sweden and Poland, it is marking its supposed sphere of influence and unambiguously threatening NATO. All this was not a response to a supposed transgression by NATO and the European Union, but a conscious decision by the political leadership in Moscow to re-establish Russia as an influential world power.

In trying to answer the question of what a sustainable strategy of deterrence for this Third Nuclear Age should look like, one might be tempted to simply combine the lessons of the two previous ages—nuclear deterrence of a nuclear power in the Cold War connected with concepts for the deterrence of nonstate or irrational actors. This solution falls short. There are fundamental differences with the situation in the former East-West conflict. While the Warsaw Pact at the time, to some extent, outmatched NATO in terms of conventional power, Moscow's conventional capabilities today are clearly inferior to those of the United States and its allies, a fact that Russia is well aware of. Russian military planning for a potential conflict in Europe is thus focused on preventing U.S. support of its NATO allies and blocking the deployment of U.S. armed forces across the Atlantic. In military jargon, this is referred to as "A2/AD" (Anti Access / Area Denial). Russia also considers its nuclear arsenal as a useful military substitute for its lack of conventional weapons capability.

Moreover, North Korea has developed into an additional factor of instability and irrationality. While Pyongyang's first nuclear test was conducted as early as 2006, it remained unclear for a long time whether the regime would actually be capable of producing functioning nuclear weapons. After three more nuclear tests in 2009, 2013 and 2016, there is hardly any doubt. Although knowledge about the status of North Korea's nuclear weapons program is still fragmented, Pyongyang could in a few years possess more nuclear warheads than France or the United Kingdom. A largely erratic actor consumed by the paranoid fear of losing power has joined the nuclear club.

This raises a number of radically new issues regarding the role of nuclear weapons in the Third Nuclear Age. For example, how can Russia be deterred? It is an obviously declining power as it has no economic basis to back up its claim to global significance and is inferior in military terms. Russia's weakness is less a result of low energy prices than of its decades-long failure to take necessary economic, political and social steps towards modernization. It is very likely that Russia will not be able to fulfill the needs of its people a few years from now, which might lead to destabilization or even disintegration. Practicing nuclear deterrence on declining powers is generally difficult because it is likely that the inferior opponent will panic or behave irrationally. This similarly applies to North Korea, although the level of irrationality in this case is dramatically higher.

Another question is—will there still be any treaty-based nuclear arms control in the Third Nuclear Age? If Russia sees its nuclear weapons as a functional part of its armed forces that can be used to compensate for deficiencies in its conventional posture, it will have little interest in reducing this potential. Since a number of outdated systems are due to be phased out, there may still be some decrease in the strategic nuclear arsenals of both the United States and Russia. However, this is another area where Russia now refuses to share information. In November 2014, Russia declared that it would no longer participate in the annual Russian-American summits on nuclear safety. One month later, Russia announced its withdrawal from the bilateral cooperation program designed to increase nuclear safety under the so-called Nunn-Lugar Act. Since 1991, the United States has provided considerable financial and material support for the safe scrapping and disposal of Russia's surplus nuclear weapons and nuclear submarines. The purpose of this program designed by the two U.S. Sens. Sam Nunn and Richard Lugar was to prevent radioactive substances, nuclear weapon elements and nuclear expertise from falling into the wrong hands.

When it comes to tactical nuclear weapons in Europe, the chances of concluding reduction treaties are virtually zero because Russia sees them as a “usable” part of its military’s ability to balance NATO’s conventional superiority. Instead, there are signs that Russia is circumventing the 1987 Intermediate-Range Nuclear Forces Treaty (INF) by stationing new systems. Likewise, NATO’s Eastern European members have little interest in a withdrawal of the few American nuclear weapons stationed in Europe. They are seen as a symbol of America's alliance commitments.

In the Asia Pacific, disarmament is even more unlikely since China's thirst for power is increasing tensions in the region and because arms control is not a common concept in the minds of the political elite. Why dismantle nuclear arsenals that one has spent so much money and effort on? Also, the states in this region have never learned the traumatic lesson of the Cuban Missile Crisis, in which two nuclear powers were gazing into the abyss of mutual annihilation. The idea of a nuclear-free world, which has been upheld for years and could allegedly be realized through good will and a genuine intention to disarm, now seems to be off the table for good. However, many experts now point out that the proposal made by the U.S. president was an illusion in the first place—gleefully believed without there ever being a realistic chance of implementation.

A further question to be answered is how can future deterrence strategies be effectively combined with sustainable crisis communication? If Russia continues to launch nuclear bomber aircraft as an implicit threat or in order to mark its supposed sphere of influence, send nuclear submarines to foreign coastal waters or simulate nuclear strikes against neighboring countries, then the risk of misunderstanding and accidents will increase. In 2014 alone, fourteen risk or high-risk incidents (i.e., entailing a considerable risk of escalation) occurred between Russian and Western aircraft or ships. What security precautions must be taken in order to prevent an unwanted military confrontation—be it conventional or even nuclear?

Another open question is: what effects will the missile defense system currently being set up by NATO have regarding the requirements for a credible system of nuclear deterrence? Since President Ronald Reagan's Strategic Defense Initiative in the early 1980s, there have been worldwide efforts to establish capabilities that can be used to neutralize approaching missiles. The discussion about whether such a defense capability would undermine the idea of deterrence—whoever shoots first dies second—and therefore also endanger international stability dates back to the same time. Any state that successfully sets up a complete defense umbrella would no longer need to fear nuclear retaliation and could therefore aggressively threaten other states. For a long time, this discussion was of limited relevance, because a perfectly functioning strategic missile defense system seemed difficult to implement—it was the equivalent of hitting a rifle bullet with another rifle bullet.

Meanwhile, systems of this kind have become a reality. With its Iron Dome air defense system, Israel has managed to successfully detect and shoot down most of the short-range missiles launched by Hamas in the Gaza Strip, even though they are only in the air for a few minutes. NATO is also procuring a defense system in several stages that uses U.S. interceptor missiles and also integrates the existing radar and sensor systems of the European alliance partners.

Moscow has been suspicious for a long time, arguing that the missile defense system would ultimately be aimed against Russia and that it would diminish its ballistic potential. Moscow has also stated that this would endanger strategic stability. NATO has always pointed out that a missile defense system is genuinely a defensive weapon that only takes effect after an opponent has launched an attacking weapon. Whoever criticizes missile defense as a fundamental idea should therefore answer the question whether he wants to retain the option to attack. Nuclear warheads can also be delivered with other means that are not affected by missile defense systems—e.g., aircraft and cruise missiles. In view of debates such as these, the connection between nuclear deterrence and missile defense is quite obvious and should therefore be taken into account in strategic considerations.

Finally, there must be a debate about how nuclear cooperation between NATO's three nuclear powers—the United States, Britain and France—can be improved in order to achieve a coherent deterrence strategy. There has always been nuclear cooperation between Washington and London. Britain and France have considerably stepped up their nuclear relations with the Lancaster House agreement of 2010. Even France and the United States discretely cooperate on nuclear matters now and then. What is missing is trilateral coordination that goes beyond an occasional exchange on nuclear forensics as mentioned above. France, while apparently not generally opposed to such cooperation, does not want it to be conducted in the relevant NATO bodies such as the Nuclear Planning Group.

Faced with a changed nuclear reality and a multitude of unanswered questions, NATO will have to put nuclear deterrence back on the agenda. NATO does have a current nuclear strategy, which is enshrined in a document with the cumbersome title Deterrence and Defense Posture Review. However, this document was approved at the NATO Summit in Chicago in 2012, and it is based on two fundamental assumptions that no longer apply today: Russia is a partner of NATO and will not threaten to use its nuclear weapons against NATO. Meanwhile, Moscow has ended its partnership with NATO and, in addition, is also simulating the use of nuclear weapons against neighboring countries in military exercises. NATO will therefore inevitably be forced to redraft its nuclear strategy.

Since this is a controversial subject in some member states, it will be difficult to reach an agreement on the much-needed nuclear strategy debate before the NATO Summit in Warsaw in July 2016. But after this meeting of allied heads of state and government, the nuclear question of how to deter whom and by what means must be up for discussion.

This is no reason for nuclear alarmism. Despite the tensions with Russia, nuclear weapons will not regain the significance they had as a currency of power in the Cold War. Their numbers have been dramatically reduced in the past decades, at least in the relations between Russia and the United States, and it is unlikely that there will be a new nuclear arms race. Moreover, nuclear deterrence is only a small part in the overall spectrum of security provision. Effective and deployable conventional armed forces, as well as the will to cooperate despite existing differences, are at least as important for the security of the NATO member states and for the stability of Europe.

That is why the upcoming nuclear debate should not be focused on new or more modern nuclear weapons, but on a coherent political concept that fulfills NATO's own requirements and is also regarded as credible by a potential opponent. Besides clear political statements, this also includes exercises and simulations that are designed to test the procedures and nuclear decision processes. Because one thing is clear: the challenges of the Third Nuclear Age will not be met using the formulas of the previous two.

Karl-Heinz Kamp is the president of the Federal Academy for Security Policy in Berlin. This article reflects the personal opinion of the author.

Image: Wikimedia Commons/U.S. Energy Department.