Nuclear weapons exist because of a chain of events that began with a scientific discovery in 1938, accelerated under the pressures of World War II, and then became locked into global politics through a logic that made them nearly impossible to give up. What started as a race to beat Nazi Germany to a devastating new technology became, within two decades, the foundation of how major powers keep the peace. Today, nine countries hold roughly 12,241 nuclear warheads, and every one of those governments believes the weapons are essential to its survival.
The Science That Made It Possible
In December 1938, two German chemists, Otto Hahn and Fritz Strassmann, were bombarding uranium with neutrons in a Berlin laboratory when something unexpected happened. Instead of changing slightly, as most elements did under neutron bombardment, the uranium nuclei broke into two roughly equal pieces. The products weighed less than the original uranium nucleus. That missing mass, as Albert Einstein’s famous equation predicted, had been converted into energy.
Hahn’s former colleague Lise Meitner, a physicist who had fled Nazi Germany for Sweden, worked out the math with her nephew Otto Frisch. The energy released was enormous, far beyond any chemical reaction. Frisch borrowed a term from biology, “binary fission,” and called the process fission. But the truly alarming detail came next: splitting a uranium atom also released additional neutrons. Those neutrons could slam into neighboring uranium atoms and split them too, releasing still more neutrons and still more energy. A chain reaction. In theory, a single starting event could cascade into an explosion of extraordinary power.
Why the First Bombs Were Built
The timing of this discovery mattered as much as the discovery itself. Nuclear fission was identified in a German lab just months before World War II began in Europe. Allied scientists, many of them refugees from fascism, immediately recognized the military implications. If Nazi Germany could harness a chain reaction, it could build a weapon capable of destroying entire cities.
That fear drove the United States to launch the Manhattan Project, a secret program to build an atomic bomb before Germany could. The project began as a race against one of the most oppressive regimes in modern history. Tens of thousands of scientists, engineers, and workers participated, and the effort succeeded in the summer of 1945, producing the bombs dropped on Hiroshima and Nagasaki. The original purpose was straightforward: build the weapon before the enemy does, then use it to end the war.
How Deterrence Changed the Equation
Once the Soviet Union tested its own bomb in 1949, the question shifted. Nuclear weapons were no longer a tool one side could use with impunity. They became something stranger: weapons whose primary purpose was to never be used. This is the core idea behind nuclear deterrence. You maintain the ability to inflict catastrophic damage on an adversary so that the adversary never attacks you in the first place.
Deterrence rests on two pillars: capability and credibility. Having the weapons is not enough. Your opponent must believe you would actually use them. That means communicating your intent clearly and maintaining forces that could survive a first strike and still retaliate. If both sides in a conflict can do this, the result is what strategists called Mutually Assured Destruction, or MAD. Neither side can launch a nuclear attack without guaranteeing its own annihilation.
The logic of MAD is counterintuitive. It treats the vulnerability of cities as a stabilizing force. If both sides know their populations are hostage to the other’s weapons, neither side has an incentive to strike first. Submarine-launched ballistic missiles became a key part of this equation because they were mobile, nearly impossible to detect, and capable of surviving even a massive surprise attack. Their very invulnerability made them stabilizing. No enemy could hope to destroy them all before they fired back.
The Nuclear Triad
The United States and Russia both maintain what’s called a nuclear triad: weapons delivered by land-based missiles, submarine-launched missiles, and bombers. Each leg of the triad serves a different strategic purpose, and together they create a problem no attacker can solve.
Land-based intercontinental ballistic missiles sit in hardened underground silos, dispersed across wide areas. They are the most responsive option, ready to launch on short notice, and an adversary would need to commit a staggering number of warheads to destroy them all. Ballistic missile submarines are the most survivable leg. They patrol the oceans silently, and finding one is considered nearly impossible with current technology. Even if every land-based missile and bomber were destroyed in a surprise attack, submarines could still deliver a devastating retaliatory strike. Bombers add flexibility. Unlike missiles, they can be recalled after launch, giving decision-makers more time and more options in a crisis.
About 2,100 warheads globally are kept on high operational alert on ballistic missiles at any given time, ready to launch within minutes.
Why Countries Still Build Them
If nuclear weapons exist primarily to prevent their own use, why do countries continue to maintain and modernize them? Several reasons keep the cycle going.
First, the security environment keeps changing. Russia launched its most extensive nuclear modernization program since the Cold War after 2011. China is in the middle of a significant expansion, growing its arsenal from an estimated 500 to roughly 600 warheads in a single year. North Korea continues testing ballistic missiles with increasing range, working toward the ability to strike the U.S. homeland and already capable of reaching South Korea and Japan. Each country’s modernization pushes others to respond.
Second, the weapons themselves age. Components in warheads originally designed for much shorter lifespans are reaching the end of their extended service lives. Maintaining a reliable arsenal requires periodic rebuilding and upgrading of delivery systems that must remain in service for decades.
Third, nuclear weapons serve a diplomatic function beyond deterring direct attack. The United States extends its nuclear umbrella over allies in Europe and Asia, promising to defend them with nuclear weapons if necessary. Countries like Japan, South Korea, and the United Kingdom have relied on this arrangement, and in return, they have either not developed their own nuclear arsenals or kept them small. If the U.S. nuclear deterrent lost credibility, some of these countries might pursue their own weapons, potentially making the world less stable rather than more.
The Agreements Meant to Limit Them
The Treaty on the Non-Proliferation of Nuclear Weapons, or NPT, has been the main international framework governing nuclear weapons since 1968. It rests on three pillars: preventing the spread of nuclear weapons to additional countries, committing existing nuclear states to work toward disarmament, and preserving the right of all countries to use nuclear energy for peaceful purposes. Nearly every nation on Earth has signed it.
The treaty has had real successes. Dozens of countries that could have built nuclear weapons chose not to. But the disarmament pillar remains largely unfulfilled. The five original nuclear-armed states recognized by the treaty (the U.S., Russia, the U.K., France, and China) still possess the vast majority of the world’s warheads, and four additional countries (India, Pakistan, Israel, and North Korea) developed weapons outside the treaty framework entirely.
The Self-Reinforcing Logic
The simplest answer to “why do nukes exist” is that no country with nuclear weapons has found a way to safely give them up. The technology cannot be uninvented. Any nation that disarmed completely would have to trust that every other nuclear-armed state would do the same, and that no new state would build one in the future. That level of trust does not exist in international politics.
So the weapons persist, not because anyone believes nuclear war would be acceptable, but because each nuclear-armed state believes that possessing them is the most reliable way to ensure it never happens. The roughly 12,241 warheads spread across nine countries represent a bet, maintained for over 80 years now, that the fear of total destruction is the most effective guarantee of peace between major powers. It is an uncomfortable logic, but it is the one the world has operated on since 1945.