EXPLAINER: Nuclear weapons – a threat to many, possessed by few

Nuclear weapons remain among the most powerful and feared tools in global geopolitics — deadly enough to level cities in seconds, yet only possessed by a handful of countries. Eight decades after they were first used in warfare, fears of a renewed arms race are resurfacing amid growing tensions.

Nuclear weapons are the most destructive arms on Earth. 

They release enormous energy through nuclear fission — the splitting of atoms — or, in the case of hydrogen bombs, a combination of fission and fusion. 

The bombs dropped on Hiroshima and Nagasaki 80 years ago remain the only nuclear weapons used in conflict.

The device in Hiroshima killed around 78,000 people instantly in 1945, with the total deaths reaching about 140,000 by the year’s end. In Nagasaki, it killed around 39,000 to 74,000 people.

"The weapon that destroyed Hiroshima back in 1945 had a yield of about 15 kiloton. So by today's standard, that weapon would be considered a low yield warhead, even though it destroyed an entire city. But today, most weapons typically have yields in several hundreds of kilotons," said Hans Kristensen, Director of the Nuclear Information Project at the Federation of American Scientists.

Modern warheads are significantly more advanced, smaller, and capable of being delivered by missile over vast distances.

Who has nuclear weapons?

Nine countries currently possess nuclear weapons, but the majority remain in the hands of two powers.

Russia holds around 4,300 nuclear weapons, while the U.S. has roughly 3,700, in addition to thousands of retired warheads awaiting dismantlement.

"These two countries are the ones that have by far the most nuclear weapons. And that has always been the case. So part of it is because of their experience with the Cold War, the role and the arsenals that they developed at the time, the strategies, etc." Kristensen said.

China is believed to hold the third-largest stockpile, though still far behind the top two powers.

Britain and France follow with approximately 250 to 300 warheads each. India and Pakistan are estimated to have around 170 each, while Israel is thought to possess just under 100.

North Korea is believed to have the smallest arsenal, with roughly 50 nuclear warheads, Kristensen said.

Are there rules to limit them?

The Treaty on the Non-Proliferation of Nuclear Weapons (NPT), in force since 1970, is the primary international agreement aimed at limiting the spread of nuclear arms. The NPT's three pillars are nonproliferation, disarmament, and peaceful uses of nuclear energy. 

Based in Vienna and operating under the United Nations, the International Atomic Energy Agency (IAEA) works with more than 170  countries to promote the peaceful use of nuclear energy while enforcing the rules of the NPT.

It recognises five nuclear-weapon states — the U.S., Russia, China, France, and Britain — and obliges them to work toward disarmament.

Non-nuclear signatories commit to using nuclear technology solely for peaceful purposes, though they are permitted to research and develop nuclear energy.

What about countries outside the NPT? 

Four countries with nuclear weapons — India, Pakistan, Israel, and North Korea — are not bound by the NPT in the same way. 

While Israel has never confirmed its arsenal, it is widely believed to possess warheads. 

India and Pakistan have openly tested nuclear weapons. 

North Korea is the only country to have left the NPT and then developed nuclear weapons, conducting its first test in 2006.

Is Iran next?

Iran remains a key concern for Western powers. It is enriching uranium to 60% purity — near the 90% required for weapons-grade material according to the International Atomic Energy Agency (IAEA).

"They've detected signs that scientists and engineers in the Iranian system have started examining options for how they could speed up the development of nuclear weapon, if the Iranian leadership decided that they should go for a nuclear weapon," explained Kristensen.

In 2018 President Donald Trump pulled the U.S. out of the Iran agreement and Kirstensen added that, "the Iranians have, not surprisingly, increased their inventory." 

Iran insists its intentions are peaceful and cites its rights under the NPT. 

However, Saudi Arabia has hinted it may seek its own arsenal if Iran builds one, stoking fears of a regional arms race.

Are we in a new nuclear era?

With the collapse of arms control treaties, increasing mistrust between major powers, and ongoing modernisation of arsenals, analysts warn of a return to Cold War dynamics.

Nuclear arsenals are constantly evolving as countries modernise their stockpiles, often introducing new types of warheads and delivery systems. The extent and nature of these upgrades vary by country.

Major nuclear powers such as Russia, the United States, and, to a lesser degree, Britain and France, have developed advanced and compact warheads with global reach. The U.S. and Russia, in particular, maintain diverse arsenals tailored to a range of strategic objectives.

The global fallout of nuclear testing

Nuclear testing has left deep scars across the globe — from the Marshall Islands, where U.S. detonations exposed islanders to dangerous radiation, to French Polynesia, where France conducted nearly 200 atmospheric and underground tests.  

In the United States, hundreds of tests at the Nevada Test Site contaminated surrounding areas and sickened so-called "downwinders." 

North Korea’s underground tests in the 21st century have raised new fears of geological and environmental damage.

One of the most severely impacted regions is Kazakhstan, where the Soviet Union carried out 456 nuclear tests at the Semipalatinsk Test Site between 1949 and 1989. These included more than a 100 atmospheric detonations.

Public resistance

Nearly 80 years after the bombings of Hiroshima and Nagasaki, public opposition to nuclear weapons remains strong, with survivors and campaigners continuing to press for disarmament.

According to AP News, many of the remaining 100,000 hibakusha — atomic bomb survivors — in Japan are increasingly vocal as nuclear threats rise globally. 

Meanwhile, in the United Kingdom, plans to expand its nuclear deterrent have sparked a wave of protests.

According to the Guardian, campaign groups such as the Campaign for Nuclear Disarmament (CND) and the Campaign Against Arms Trade are organising mass demonstrations, reminiscent of the Greenham Common peace camp of the 1980s.

The UK government’s decision to purchase 12 American-made F-35A fighter jets — capable of carrying U.S. B61-12 nuclear gravity bombs — has reignited fears of a renewed nuclear presence on British soil.

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Explainer nuclear weapons Hiroshima and Nagasaki Hans Kristensen Global Security Cold War USA Russia China Japan Iran North Korea Non-Proliferation of Nuclear Weapons treaty