Why do nuclear weapons deter war?

The popular answer is at best incomplete

The effect of most new military technologies is to increase combatant effectiveness. Nuclear weapons are unusual: they deter war. It is widely believed that they are responsible for the Long Peace, the period from the Second World War to the present day marked by an unprecedented lack of great power conflict.

Why do nuclear weapons deter war, rather than serving as merely the most potent weapons in a country’s arsenal? The traditional explanation is: nuclear weapons raise the cost of defeat from merely losing to total annihilation. The expected utility of going to war plummets because the downside becomes so large. Kenneth Waltz argues (emphasis mine):

Countries armed with conventional weapons go to war knowing that even in defeat their suffering will be limited. … If countries armed with nuclear weapons go to war with each other, they do so knowing that their suffering may be unlimited. … In a conventional world, one is uncertain about winning or losing. In a nuclear world, one is uncertain about surviving or being annihilated.¹

In the first chapter of The Myth of the Nuclear Revolution, Keir Lieber and Daryl Press contend that Waltz’s reasoning is “simply wrong”. 

• First, they argue that war in the pre-nuclear era used to be just as devastating for the losing side—both civilians and their rulers. Despite this, great power conflict persisted. So, the deterring ability of nuclear weapons must arise from something more than their mere destructiveness.

• Second, they provide a more plausible theory of nuclear deterrence: it’s not that nuclear weapons raise the cost of a defeat. Rather, they make victory impossible, so that going to war becomes pointless.

This post summarizes both these arguments.

Defeat in conventional war used to be devastating

In the pre-nuclear era, a loss in a war was usually followed by “mass enslavement, torture and slaughter.” To illustrate this, Lieber and Press offer a few examples from ancient and modern history:

• Thucydides’ account of the Peloponnesian War matter-of-factly describes the victorious Athenians putting “all the men of military age” in Melos to death, and “[selling] the women and children as slaves.”  

• Alexander the Great massacred or enslaved the citizens of defeated cities like Persepolis, Tyre and Thebes.

• When Romans defeated Carthage, they burned down the city, massacred all men, and enslaved the women and children. This wasn’t unusual behavior following a Roman victory.

• The Mongols brutally crushed revolts to make an example out of them for neighboring peoples.

• More recently, the Second World War saw destructive behavior from nearly all sides: the Nazi Wehrmacht carried out genocide, and the Red Army brutalized the residents of Berlin in turn; and Japan’s war crimes during the conquest of China and Korea such as the Rape of Nanking, chemical and biological warfare, the man-made Yellow River flood and the enslavement of comfort women was met by the US burning down “sixty-four of the sixty-six largest cities in Japan” even before dropping the atomic bombs on Hiroshima and Nagasaki. 

Copper engraving depicting a naval battle near Corinth during the Peloponnesian War, via AKG

Despite the high costs of defeat, leaders continued to wage wars. This is even more surprising when you consider that defeat was often personally costly to military commanders:

• The Melian heads of state were put to death with their countrymen.

• After being defeated in a historically bloody civil war, the Ming emperor and his senior advisors killed themselves to avoid what they evidently believed would be a worse fate at the hands of their enemies.

• After a civil war, the victorious Tairas tried to wipe out the rival Minamoto clan’s leading family. Unfortunately for them, they were not thorough enough and spared three children. One of them grew up to defeat the Tairas and became Japan’s first shogun. This episode probably illustrates why throughout history, the victor has insisted on wiping out its rival’s royal family.

• The tsar Nicholas and his family were assassinated after Russia lost the First World War. Lieber and Press say that by this time, “murdering a defeated enemy’s children was standard practice among hereditary monarchs.”

• The suicide of Hitler and other Nazi leaders as the Soviets closed in on Berlin during the end of the Second World War is well-known.

• Saddam Hussein was hanged on the gallows.

• Muammar Gaddafi was pulled from his hideout inside a drainage pipe and lynched.

Lieber and Press ask, “[c]ompared with the old-fashioned punishment—meted out on the battlefield or on the torture rack—what is worse about a bright flash and a quick death?” There should be a better explanation for the deterring ability of nuclear weapons than their mere destructiveness.

The logic of stalemate

Nuclear weapons make victory impossible.

In the pre-nuclear era, a cheap victory wasn’t exactly uncommon, even in great power conflicts:

• The British victory over the Spanish armada, which established London as the world’s naval superpower for decades, came at the cost of eight burnt fireships.

• Imperial Japan won decisively in the Russo-Japanese war, earning access to China and Korea.

• The Second World War would probably have resulted in one of the most one-sided victories in European history for Nazi Germany had Hitler halted his campaign in the summer of 1940 after capturing Poland, Norway, Denmark, France, and the Low Countries.

As this list hopefully shows, the spoils of war could sometimes be tempting enough to make waging one a rational decision.

This is no longer true in the nuclear era. 

Nuclear weapons have a property that I’ll call “last legs usability”—that is, the ability to be deployed by the losing state even when it’s on its last legs in a conventional conflict. This means that total annihilation, earlier an outcome reserved for the losers, can now be inflicted on the victor with deadly ease. 

Last legs usability comes from two properties:

• Resilience: First, nuclear weapons can deliver enormous explosive force per warhead. So, for a disarming first strike to completely eliminate the threat of retaliation, practically every silo and nuclear submarine has to be eliminated. This is impractical to do (at least right now), especially due to difficulties around detecting nuclear submarines.
  Second, nuclear munitions are small. A warhead capable of destroying a fairly large city measures less than ten meters in length and weighs a few hundred kilograms.² Their small size makes nuclear weapons difficult to detect and destroy.

• Ease of delivery: Due to being small and relatively lightweight, nuclear weapons can be launched from a variety of platforms. Many states maintain a nuclear triad—land (mobile launchers on rails, heavy trucks and hardened silos), air (strategic bombers) and sea (submarine-launched ICBMs). In the past, an invading force could avoid retaliation by gaining control of the skies and the sea. Now, stealth missiles and aircraft can evade enemy radar, and submarines can attack coastal cities and ports undetected. This allows countries losing a conventional war to lethally strike back no matter whose planes patrol the skies and ships skim the seas.

Due to last legs usability, nuclear weapons make “real victory” impossible. Great powers have scarcely an incentive to go to war; even if they won a conventional campaign, they’d face deadly nuclear retaliation.

Nuclear weapons’ propensity to cause “stalemate”, and not just their potential to cause massive destruction, makes them uniquely deterring.

1. Sagan, Scott D, and Kenneth N Waltz. The Spread of Nuclear Weapons: A Debate Renewed. New York, W.W. Norton, 2003, p. 9.

2. “Fairly large city” is about 200 square kilometres. Yield-to-area destruction data is from here and bomb dimensions-to-yield data is from here.