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 Since a number of outdated systems are due to be phased out, there may still be some decrease in the strategic nuclear arsenals of both the United States and Russia.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.