How should we think about the dilemmas of leadership in a thermonuclear world?  And what can history – especially the history of how American presidents wrestled with the enormous responsibility of nuclear decision-making – tell us about our contemporary nuclear dilemmas?

Let me begin with a story from the past. Former secretary of state, Dean Acheson, purportedly advised President John F. Kennedy that his most important responsibility was to think long and hard about nuclear weapons. Acheson told JFK that he had to decide whether or not he would ever use nuclear weapons, and once he had, to never tell anyone.

Kennedy appeared to heed this advice. Declassified documents reveal that few presidents in the nuclear era made as great an effort to understand the nuts and bolts of how a nuclear war could unfold. He asked searching questions of his advisors, and even authorised a closely-held study of how a pre-emptive nuclear attack on Soviet nuclear forces would unfold and what it would accomplish. And, of course, he faced perhaps the most dangerous period in world history, when a nuclear exchange seemed frighteningly possible. Beginning with the disastrous Vienna summit and the building of the Berlin Wall in the summer of 1961, and culminating in the terrifying thirteen-day Cuban Missile Crisis, no American leader ever came closer to a thermonuclear war.

What did Kennedy think of nuclear weapons, and did he ever seriously entertain using them? I can argue it either way.

The risks he took and the strategies he embraced were quite aggressive. America’s nuclear war plans followed a certain logic – go first, go fast, go hard – so that the Soviets would be left with little or nothing in reserve to reply with. He authorised a speech by Roswell Gilpatric in the autumn of 1961 which Soviet leader Nikita Khrushchev interpreted, with some justification, as a first strike speech. The Soviet secret placement of nuclear-tipped warheads was a grave affront. And time was not on the US side – in the autumn of 1962, the United States had such overwhelming strategic nuclear superiority that a pre-emptive attack might neutralise the ability of the Soviets to respond. This window – which opened up with new American satellites allowing it to target Russian forces that were far smaller and more vulnerable than had been recognised – would close quickly. Indeed, in less than a year, military planners would tell the president that the US lived in a state of mutual vulnerability with Russia and that an American pre-emptive nuclear strike would invite unimaginable devastation upon the United States.

Does that mean, if the Russians had not pulled their nuclear forces from Cuba in the fall of 1962, that JFK would have risked nuclear war in an assault on the island? Not necessarily.

There is as much, if not more, evidence pointing in the other direction – Kennedy worked diligently to make sure nuclear weapons were under firm American and civilian command, installing permissive action links and increasing civilian controls over the bomb. During the Cuban Missile Crisis, he sought political solutions that avoided the risk of escalation, which he feared any military attack on Cuba would bring. He used his brother, the attorney general Robert F. Kennedy, to negotiate with Soviet representatives, going around some of his more hawkish advisors. While it is impossible to prove, there is evidence that JFK would have gone to great lengths to avoid any military clash, which might have led to rapid escalation.

The evidence of his desire to avoid nuclear use becomes even clearer after the United States compelled Khrushchev to remove its medium-range ballistic missiles from Cuba. When the crisis was over, he worked very hard to reduce nuclear dangers. Instead of seeking to further punish the Soviets after their irresponsible deception, he instead decided – at great domestic political cost, and to the consternation of his allies – to work with the Soviet Union to reduce nuclear dangers. He pursued the first major nuclear arms control agreement, the partial test ban treaty, signed less than a year after the Cuban Missile Crisis ended.

Why does this matter today?

Russia’s brutal invasion of Ukraine has, for the first time since the end of the Cold War and, arguably, for the first time since Kennedy’s presidency, brought back the spectre of nuclear use to the world. I want to briefly highlight several often-underappreciated dilemmas history reminds us a nuclearised world visits on international politics. This is especially important as we wrestle with the carnage in Ukraine and the highly irresponsible nuclear threats President Putin and his associates have made.

How seriously should we take such nuclear threats, and what does the past reveal about individual leaders who made – or received – them? Reactions have ranged on a spectrum, from those who have dismissed Putin’s nuclear threats as bluffs that should be ignored, to those who argue they must be taken with the utmost seriousness.

Who is right? This highlights firstly what I suggest are at least six puzzles and dilemmas about individual leadership in a thermonuclear age. The truth is, we cannot know, ex ante, how to best evaluate nuclear threats. Most of these arguments are about nuclear deterrence, which is about preventing something from happening. And given how much we argue over things that actually do happen, figuring out why something like nuclear use does not happen – until it does – is very hard.

For example, consider the question of whether nuclear weapons made the Cold War more or less stable. Did America’s nuclear weapons prevent the Soviet Union from taking over Western Europe during the Cold War? Or did the Soviets have no intention of ever coming, or were deterred by other Western actions? Did nuclear weapons provide for what the military historian John Lewis Gaddis called ‘the Long Peace,’ or, as the Berlin and Cuban Missile Crises indicate, did they bring the world close to a catastrophic thermonuclear war?

A second dilemma – thermonuclear weapons have transformed the international system, yet the decision to use them typically lies in the hands of a single individual. Great power wars of conquest and invasion, which shaped world politics for a millennia, made no sense in a thermonuclear world after the early 1950s. The consequences of nuclear use are overwhelming and catastrophic, and would affect millions, including many outside of the battle zone. There was not a political goal that was worth this cost.

Such a capability, one might think, could only be used if it went through a serious, complex process, where every stakeholder had a say. But in fact, as far as we know, the decision to use nuclear weapons usually lies in the hand of one person at the top of the system – a Biden, a Sunak, a Xi, a Macron, a Modi, a Putin. This concern about the extraordinary concentration of power in one person’s hands was heightened, understandably, when Donald Trump was US president. Indeed, the concentration in the American case is more pointed than in others because the history of American war plans – marked by pre-emptive elements – requires incredibly fast decision-making. Regardless of the reason, the idea that one person can make a decision that effects the fate of the entire planet is, to say the least, deeply concerning.

Which leads to a third dilemma. While it makes literally no strategic sense to use these weapons to achieve political ends, there is an enormous incentive to make others think you might use them to generate coercive leverage. In such a world, it is very tempting for a leader to bluff; simply a polite term for lying. This creates an incentive system where bad behaviour is possibly rewarded and responsible behaviour punished.

Compare this dynamic with the non-nuclear world. If Country A has 50 tanks, and takes on an adversary with 500 tanks, its threat to attack is not credible. But the same is not true with nuclear weapons, where the possessor of 500 nuclear weapons may be a responsible actor and signal that they will never use these terrible weapons. The person with fewer weapons may, however, be willing to make irresponsible threats to get their way. Who can tell if the person is serious or not? Given the consequences of nuclear use, doesn’t it make some sense to pay attention to the threat? Indeed, if you look at the details of Soviet Premier Khrushchev’s threats of nuclear blackmail in the late 1950s and early 1960s, one can imagine circumstances where he got away with his bluff, where the US simply conceded to avoid the danger of a nuclear war.

To be clear, this bluffing dynamic is not simply the act of dictators and despots. The United States has long based its grand strategy on signalling a willingness to use nuclear weapons first. It was arguably the threat to use nuclear weapons by Eisenhower and Kennedy that prevented Khrushchev from taking Berlin or keeping his missiles in Cuba. And President Richard Nixon on several occasions tried to put forward strategies and positions that made it appear he would be willing to use nuclear weapons. Tapes reveal he often considered the ‘madman’ theory, or the rationality of an irrational approach. The idea that his adversaries might think he was crazy enough to use them might force them, against their interests, to back down. One wonders if Nixon embraced this strategy as a result of watching how close Khrushchev came to getting away with nuclear bluffing at the end of the Eisenhower presidency.

Indeed, this highlights a fourth dilemma. One of the reasons the United States signalled a willingness to go first was in order to keep the states it protects – like Japan, Germany, and other allies – from acquiring their own nuclear weapons. It is forgotten how radical America’s nuclear non-proliferation policies are – when, in human history, has one state been able to convince another state not to acquire a technology that meets its most important, difficult goal – protecting its sovereignty and largely eliminating the danger it will be invaded and conquered? Yet American presidents have entered into a number of security arrangements to offer to protect allies from assault by nuclear-armed enemies and, in return, expose the American homeland to nuclear attack in order to protect some far-away country. These commitments drove the United States to acquire expensive nuclear delivery forces possessing accuracy, stealth, mobility, and speed, deployed in strategies that were quite forward-leaning. The radical nature of extended deterrence is rarely appreciated, though it is at the heart of the debate over Ukraine’s accession to NATO.

This highlights a fifth dilemma – nuclear weapons are tools of the weak. They flatten out other forms of power, be it conventional military power, economic prowess, or cultural attraction.  No one in the US would ever think about North Korea for a minute if they didn’t have the bomb. But that they do means a sixth-rate power with a barely-functioning economy commands the attention of the United States.

Which leads to a final dilemma, one that its difficult to prove but that I believe to be true. If any American president could wave their hand and make the world non-nuclear, with one possible exception – Richard Nixon – they would have.

Why? First, imagine the terrible individual responsibility. You possess the power to use a weapon that could incinerate countries and kill tens of millions, if not end life on the planet. Your adversaries are often ruthless, authoritarian tyrants. And the choice to use the weapons will likely not come over a direct threat to the American homeland – neither Mexico nor Canada will invade you, and the Atlantic and Pacific Ocean provide protection from overseas invaders. Your choice to use the bomb, and expose your own citizens and society to destruction, will be made when some faraway ally is attacked. Just as bad, you strongly sense that at the end of the day, you would never authorise nuclear use, short of a direct nuclear attack upon the American homeland, and even then, you aren’t sure.

Consider presidents Eisenhower and Kennedy in the late 1950s and early 1960s, facing an aggressive, ruthless geopolitical and ideological adversary, committed to aggression and world revolution, led by men willing to do terrible things to their own citizens, all within living memory of another brutal regime, Nazi Germany. This, in a world where surprise attacks similar to those launched in 1941 by Japan and Hitler’s Germany, though with thermonuclear weapons, seemed plausible. Eisenhower and Kennedy’s reticence came at a time when the United States actually possessed overwhelming nuclear superiority, which both understood was a ‘wasting asset’.  Still, neither president came close to using them during a dangerous crisis. In retrospect, one wonders if America’s nuclear promises were, in fact, a giant bluff.

A world without nuclear weapons would be one where you slept better at night and could deploy other forms of America’s power more easily. If you are an American president, why would you want a world where terrible weapons empowered your otherwise weak enemies, and gave you sole responsibility for doing something horrendous, essentially based on the lie that you would use these weapons to protect far away allies?  Yet, needless to say, nuclear weapons exist, are likely to be part of the leading power’s arsenals for quite some time, and the dilemmas and puzzles around them are unlikely to be resolved.