Nuclear proliferation refers to the spread of nuclear weapons to countries that are not officially recognized as nuclear-weapon states by the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). This spread happens through the sharing of materials used to make nuclear weapons, as well as the technology and skills needed to create them. In modern times, it also includes the transfer of nuclear weapons to groups that are not governments. Many countries, with and without nuclear weapons, oppose proliferation because they worry that more nuclear-armed nations could increase the risk of nuclear war, harm international relations, or challenge the principle of state sovereignty. Supporters of deterrence theory argue that limited nuclear weapons use among some countries may reduce conflicts by creating a balance of power.

Nuclear weapons research began during World War II, with the United States, United Kingdom, and Canada working together, while Germany, Japan, the Soviet Union, and France conducted separate studies. The United States was the first and only country to use nuclear weapons in war, dropping two bombs on Japan in August 1945. After surrendering, Germany and Japan stopped all nuclear weapon research. A nuclear arms race followed, with the United States and the Soviet Union competing to develop and test weapons. The Soviet Union conducted its first nuclear test in 1949. Seven other countries developed nuclear weapons during the Cold War. The United Kingdom and France, both members of NATO, created fission and fusion weapons in the 1950s and 1960s, respectively. China developed both types of weapons during the Sino-Soviet split.

Five countries—Israel, South Africa, India, Pakistan, and North Korea—are believed to have nuclear weapons, but are not officially recognized as nuclear-weapon states under the NPT. South Africa ended its nuclear program and joined the NPT, while the other four countries are not members. A criticism of the NPT is that it treats some countries unfairly, as only those that tested nuclear weapons before 1968 are recognized as nuclear-weapon states, while others must give up nuclear weapons to join the treaty.

Many other countries started nuclear weapons programs but did not complete them. These include Yugoslavia, South Korea, Libya, Brazil, Iraq, Iran, and Syria. Some countries, like modern Iran and Japan, are believed to have the ability to quickly develop nuclear weapons if needed. Nuclear proliferation is linked to civilian nuclear power because facilities used to process nuclear fuel can also produce materials for weapons. It is also connected to the spread of nuclear weapons delivery systems, such as ballistic missiles.

History of nuclear non-proliferation efforts

Early efforts to stop the spread of nuclear weapons included strict government secrecy, the wartime collection of known uranium supplies (the Combined Development Trust), and sometimes direct actions like the bombing of a heavy-water facility in Norway, which was believed to be part of a German nuclear program. These actions began right after scientists discovered how to split atoms and realized the military power of nuclear energy. None of these efforts were made public because the development of nuclear weapons was kept secret until the bombing of Hiroshima.

After World War II, serious international efforts to stop the spread of nuclear weapons started. In 1946, the Truman Administration proposed the Baruch Plan, named after Bernard Baruch, who was the first American representative to the United Nations Atomic Energy Commission (UNAEC). The Baruch Plan, which was based on the Acheson–Lilienthal Report from the same year, suggested that the United States would safely remove and destroy its nuclear weapons after all countries worked together to achieve two goals: (1) creating an "international atomic development authority" that would own and control all nuclear materials and activities used for military purposes, and (2) setting up a system of automatic penalties that even the United Nations Security Council could not stop. These penalties would punish countries trying to build nuclear weapons or materials.

Baruch’s call to destroy nuclear weapons appealed to basic moral and religious ideas. In one speech to the United Nations, he said, "Behind the dangers of the new atomic age lies a hope that, if we believe in it, can lead us to peace. If we fail, we will leave every person enslaved by fear. We must choose between world peace or world destruction. We must answer the world’s need for peace and security." This speech helped begin the study of nuclear ethics, which many experts and scholars have explored.

Although the Baruch Plan had strong support worldwide, it did not pass through the UNAEC because the Soviet Union planned to block it in the Security Council. However, the plan remained official American policy until 1953, when President Eisenhower introduced the "Atoms for Peace" proposal to the United Nations General Assembly. This proposal eventually led to the creation of the International Atomic Energy Agency (IAEA) in 1957. Under the "Atoms for Peace" program, thousands of scientists from around the world were trained in nuclear science and then sent back to their countries, where many later worked on secret weapons programs.

Efforts to create an international agreement to limit the spread of nuclear weapons began in the early 1960s, after four countries (the United States, the Soviet Union, the United Kingdom, and France) had developed nuclear weapons. These efforts slowed in the early 1960s but started again in 1964 after China tested a nuclear weapon. In 1968, governments at the Eighteen Nation Disarmament Committee (ENDC) completed the text of the Nuclear Non-Proliferation Treaty (NPT). In June 1968, the United Nations General Assembly approved the NPT with Resolution 2373 (XXII), and in July 1968, the NPT was opened for countries to sign in Washington, D.C., London, and Moscow. The NPT became official in March 1970.

Since the mid-1970s, the main goal of non-proliferation efforts has been to keep international control over materials and technologies needed to build nuclear weapons, because these are the hardest and most expensive parts of such programs. The main materials controlled are highly enriched uranium and plutonium. While acquiring these materials is difficult, the scientific and technical tools needed to build simple nuclear weapons are within the reach of industrialized nations.

Since its creation by the United Nations in 1957, the International Atomic Energy Agency (IAEA) has worked toward two goals that sometimes conflict: promoting the use of nuclear energy for peaceful purposes and preventing the use of nuclear energy for weapons or other harmful purposes. The IAEA now follows a safeguards system outlined in Article III of the NPT, which ensures that nuclear materials and related technologies are used only for peaceful purposes and do not help spread nuclear weapons. Some argue that the spread of nuclear weapons has been limited because nuclear powers have offered security guarantees to other countries through treaties, but other factors, such as a country’s pride or past experiences, also influence whether a country builds nuclear weapons.

Dual-use technology

Dual-use technology means that some civilian nuclear power tools and materials can also be used for military purposes. Many parts of the nuclear fuel cycle allow nuclear materials to be diverted for making nuclear weapons. This can turn a nuclear power program into a way to build atomic bombs or hide a secret weapons program. The situation with Iran’s nuclear activities is an example of this issue.

Many United Nations and U.S. organizations warn that building more nuclear reactors increases the risk of nuclear weapons spreading. A key goal for American and worldwide security is to reduce these risks as nuclear power expands. If this growth is not carefully managed or if efforts to control risks fail, the future of nuclear energy could become very dangerous. To safely develop and manage nuclear power programs, countries must have strong domestic systems that support proper nuclear operations and management.

International cooperation

At present, 189 countries have joined the Treaty on the Nonproliferation of Nuclear Weapons, also called the Nuclear Non-Proliferation Treaty (NPT). These include the five nuclear-armed countries recognized by the NPT: the People's Republic of China, France, the Russian Federation, the United Kingdom, and the United States.

Notable countries that have not signed the NPT include Israel, Pakistan, and India. India and Pakistan have tested nuclear weapons, and Israel is believed to possess nuclear weapons but has not officially admitted it. North Korea was once a signatory but left the treaty in January 2003. Some people disagree about whether this withdrawal was legal. On 9 October 2006, North Korea claimed it tested a nuclear device, which led to sanctions from the United Nations Security Council.

The International Atomic Energy Agency (IAEA) was created on 29 July 1957 to help countries use nuclear energy for peaceful purposes. It also ensures that countries follow their promises under the NPT. The IAEA reports to both the United Nations General Assembly and the Security Council.

The IAEA regularly checks nuclear facilities to confirm that the information provided by countries is correct. It examines materials, takes samples, and analyzes them. Safeguards are designed to prevent the misuse of nuclear materials by making it easier to detect problems early. These safeguards are supported by rules that control the export of sensitive nuclear technology from countries like the United Kingdom and the United States through groups like the Nuclear Suppliers Group. The IAEA’s main concern is ensuring that uranium is not enriched beyond what is needed for peaceful uses and that plutonium produced in reactors is not made into weapons.

Traditional safeguards involve tracking and controlling nuclear materials. This is a key part of the system that ensures uranium is used only for peaceful purposes.

Countries that have joined the NPT agree to allow the IAEA to apply safeguards. This means nuclear facility operators must keep detailed records of all nuclear material movements and transactions. Over 550 facilities and many other locations are regularly inspected, and their records and materials are reviewed. Inspections by the IAEA are supported by tools like surveillance cameras and other monitoring equipment.

These inspections help detect if nuclear materials are being used for purposes other than peaceful ones. The system includes three main parts:

• Material Accountancy – tracking all nuclear material movements, including sampling, on-site inspections, and reviewing records.
• Physical Security – limiting access to nuclear materials at nuclear sites.
• Containment and Surveillance – using seals, cameras, and other tools to detect unauthorized activity or tampering, along with on-site checks.

All NPT countries that do not possess nuclear weapons must accept full safeguards. In the five nuclear-armed countries and the non-NPT countries (India, Pakistan, and Israel), safeguards apply only to specific facilities. IAEA inspectors regularly visit these facilities to check records and ensure accuracy.

The NPT itself cannot be enforced by the IAEA, and countries cannot be forced to join the treaty. However, as seen in the cases of Iraq and North Korea, safeguards can be supported by diplomatic, political, and economic actions.

Traditional safeguards were good at verifying declared nuclear activities, but in the 1990s, attention shifted to activities that might not have been reported. Iraq, which was an NPT member, secretly built equipment to enrich uranium for weapons. North Korea used research reactors and a nuclear reprocessing plant to produce weapons-grade plutonium.

A weakness of the NPT system was that some activities, like using indigenous uranium or building facilities without declaring them, were hard to detect. Iraq, as an NPT member, was required to report all facilities but did not do so. These activities were eventually discovered and controlled through international efforts, including military action in Iraq.

In North Korea, activities occurred before it signed the NPT. A promise to provide commercial power reactors temporarily eased tensions, but North Korea later left the NPT and claimed to have nuclear weapons.

In 1993, a program was started to improve the safeguards system. A model protocol was agreed to in 1997, which gave the IAEA more tools to find undeclared nuclear activities.

Improvements included:
– Using existing legal authority to inspect facilities and check records.
– Requiring new legal agreements, called Additional Protocols, to allow more access and information sharing.

Key features of the Additional Protocol include:
– Providing the IAEA with more information about nuclear activities, including research, uranium and thorium production, and nuclear-related trade.
– Allowing IAEA inspectors greater access to suspect locations, even with short notice, and using techniques like environmental sampling and remote monitoring.
– Simplifying administrative processes so inspectors can work more efficiently.
– Tailoring safeguards to each country’s unique situation and nuclear materials.

As of 3 July 2015, 146 countries had signed the Additional Protocol, and 126 had fully implemented it. The IAEA also applies these measures in Taiwan. Under the Joint Comprehensive Plan of Action, Iran agreed to use the Additional Protocol. Some countries, like Egypt and Brazil, have not signed the protocol for different reasons.

The biggest risk of nuclear weapons spreading comes from countries that have not joined the NPT and have nuclear activities that are not monitored. India, Pakistan, and Israel are in this group. While some of their activities are under safeguards, others are not.

Another concern is that countries might build nuclear facilities under safeguards and later leave the NPT. Bilateral agreements may be used to manage such situations.

Unsanctioned Nuclear Activity or U.N.A

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India, Pakistan, and Israel are "threshold" countries in terms of the international non-proliferation regime. They have the ability or are quickly capable of building one or more nuclear weapons. These countries have not joined the 1970 Nuclear Non-Proliferation Treaty (NPT). Because of this, they are largely not allowed to trade in nuclear plants or materials, except for safety-related devices in a few protected facilities.

In May 1998, India and Pakistan each tested several nuclear devices underground. This increased concerns about a nuclear arms race between them, with Pakistan involving the People's Republic of China, a known nuclear weapons state. Both countries are against the NPT as it stands, and India has always criticized the Treaty since its creation in 1970, calling it unfair to non-nuclear powers.

Relations between India and Pakistan are tense and hostile, and the risk of nuclear conflict between them has long been considered high. The dispute over Kashmir is a major source of tension, as its sovereignty has been in question since 1948. There is a continuous low-level military conflict between the two countries due to Pakistan's alleged support for insurgency in India and the infiltration of Pakistani-backed militants into Indian-administered Jammu and Kashmir, along with the disputed status of Kashmir.

Both countries engaged in a conventional arms race in the 1980s, including advanced technology and equipment capable of delivering nuclear weapons. In the 1990s, the arms race accelerated. In 1994, India reversed a four-year trend of reduced defense spending, and despite its smaller economy, Pakistan was expected to increase its defense expenditures further. Both countries have lost their former supporters: India, the former USSR, and Pakistan, the United States.

However, the growth and modernization of China's nuclear arsenal, along with its assistance to Pakistan's nuclear program and, reportedly, its missile technology, have increased Indian concerns. In particular, Indian strategists believe that Pakistan is supported by China's People's Liberation Army.

Nuclear power for peaceful use is well established in India. Its civil nuclear strategy has focused on complete independence in the nuclear fuel cycle, necessary because of its rejection of the NPT. Due to economic and technological isolation after the nuclear tests in 1974, India has focused on developing fast breeder technology through extensive research at the Indira Gandhi Center for Atomic Research (IGCAR) in Kalpakkam, in southern India. Currently, India has a small fast breeder reactor and a larger Prototype Fast Breeder Reactor. This self-sufficiency includes uranium exploration and mining, fuel fabrication, heavy water production, reactor design and construction, reprocessing, and waste management. India is also developing technology to use its abundant thorium resources as nuclear fuel.

India has 14 small nuclear power reactors in commercial operation, two larger ones under construction, and ten more planned. The 14 operating ones (2548 MWe total) include:

• Two 150 MWe BWRs from the United States, which started in 1969, now use locally enriched uranium and are under safeguards,
• Two small Canadian PHWRs (1972 & 1980), also under safeguards, and
• Ten local PHWRs based on Canadian designs, two of 150 and eight of 200 MWe.
• Two new 540 MWe and two 700 MWe plants at Tarapur (known as TAPP: Tarapur Atomic Power Station).

The two under construction and two of the planned ones are 450 MWe versions of these 200 MWe domestic products. Construction has been seriously delayed by financial and technical problems. In 2001, a final agreement was signed with Russia for the country's first large nuclear power plant, comprising two VVER-1000 reactors, under a Russian-financed US$3 billion contract. The first unit is due to be commissioned in 2007. A further two Russian units are under consideration for the site. Nuclear power supplied 3.1% of India's electricity in 2000.

India's weapons material appears to come from a Canadian-designed 40 MW "research" reactor, which started in 1960, and a 100 MW indigenous unit in operation since 1985. Both use local uranium, as India does not import any nuclear fuel. It is estimated that India may have built up enough weapons-grade plutonium for a hundred nuclear warheads.

It is widely believed that the nuclear programs of India and Pakistan used Canadian CANDU reactors to produce fissionable materials for their weapons; however, this is not accurate. Both Canada (by supplying the 40 MW research reactor) and the United States (by supplying 21 tons of heavy water) provided India with the technology necessary to create a nuclear weapons program, dubbed CIRUS (Canada-India Reactor, United States). Canada sold India the reactor on the condition that the reactor and any by-products would be "employed for peaceful purposes only." Similarly, the United States sold India heavy water for use in the reactor "only… in connection with research into and the use of atomic energy for peaceful purposes." India, in violation of these agreements, used the Canadian-supplied reactor and American-supplied heavy water to produce plutonium for its first nuclear explosion, Smiling Buddha. The Indian government controversially justified this, however, by claiming that Smiling Buddha was a "peaceful nuclear explosion."

The country has at least three other research reactors, including the tiny one exploring the use of thorium as a nuclear fuel, by breeding fissile U-233. In addition, an advanced heavy-water thorium cycle is under development.

India exploded a nuclear device in 1974, the so-called Smiling Buddha test, which it has consistently claimed was for peaceful purposes. Others saw it as a response to China's nuclear weapons capability. It was then universally perceived, despite official denials, to possess or be able to quickly assemble nuclear weapons. In 1999, it deployed its own medium-range missile and has developed an intermediate-range missile capable of reaching targets in China's industrial heartland.

In 1995, the United States quietly intervened to prevent a proposed nuclear test. However, in 1998, there were five more tests in Operation Shakti. These were unambiguously military, including one claimed to be of a sophisticated thermonuclear device, and their declared purpose was "to help in the design of nuclear weapons of different yields and different delivery systems."

Indian security policies are driven by:

• Its determination to be recognized as a dominant power in the region,
• Its increasing concern with China's expanding nuclear weapons and missile delivery programs,
• Its concern with Pakistan's capability to deliver nuclear weapons deep into India.

India perceives nuclear weapons as a cost-effective political counter to China's nuclear and conventional weaponry, and the effects of its nuclear weapons policy in provoking Pakistan are, by some accounts, considered incidental. India has had an unhappy relationship with China. After an uneasy ceasefire ended the 1962 war, relations between the two nations were frozen until 1998. Since then, a degree of high-level contact has been established, and a few elementary confidence-building measures have been put in place. China still occupies some territory captured during the aforementioned war, claimed by India, and India still occupies some territory claimed by China. Its nuclear weapon and missile support for Pakistan is a major point of contention.

American President George W. Bush met with India Prime Minister Manmohan Singh to discuss India's involvement with nuclear weapons.

Breakout capability

A breakout capability refers to the ability of a country without nuclear weapons to quickly create one or more weapons with little warning.

• Japan has nuclear power plants and experience with nuclear energy. It also has a supply of plutonium that could be used to make weapons relatively quickly.
• Iran, according to some experts, may be trying to develop (or may already have) a breakout capability. This is because Iran has a stockpile of low-enriched uranium and the ability to increase its concentration to a level that could be used for weapons.

Arguments for and against proliferation

There has been much discussion among experts about whether allowing more countries to have nuclear weapons is a good idea. In the late 1950s and early 1960s, General Pierre Marie Gallois of France, who advised President Charles de Gaulle, wrote in books such as The Balance of Terror: Strategy for the Nuclear Age (1961) that simply having a nuclear weapons capability, which the French called the Force de frappe, could prevent war. He believed that spreading nuclear weapons might make the world safer.

Some well-known scholars, like Kenneth Waltz, a retired professor at the University of California, Berkeley, and John Mearsheimer, a professor at the University of Chicago, have argued in recent years that allowing some countries to have nuclear weapons could reduce the chance of war, especially in areas with conflicts. Most experts disagree with this idea, but there are two main views: one group, like Mearsheimer, supports giving nuclear weapons to certain countries, while another, like Waltz, believes that countries should be allowed to develop nuclear weapons freely, even if it causes problems.

Waltz argues that the idea of mutually assured destruction (MAD), where both sides know that using nuclear weapons would lead to total destruction, can work in all situations. He points to the Cold War as proof, saying that the United States and the Soviet Union avoided war because neither wanted to risk nuclear annihilation. He believes this logic would apply even in other parts of the world.

Other experts, like Todd Sechser and Matthew Fuhrmann, say nuclear weapons are not always helpful in preventing war. They argue that nuclear weapons are good for defense but not for attacking others. They believe nuclear proliferation might not be as harmful as people think, but they also warn that mistakes, terrorism, or sabotage could still cause problems.

Mearsheimer does not agree with Waltz’s idea that nuclear weapons always prevent war. However, he has suggested that some countries, like Germany and Ukraine in Europe after the Cold War, should be given nuclear weapons to balance power and prevent war. He predicted that without this, war could happen in Europe, as seen when Russia invaded Ukraine in 2022.

Some people argue against both letting all countries have nuclear weapons and only letting some have them. They say that the ideas behind these arguments, such as the belief that military strength is the most important concern for countries, might not be correct. Others argue that economic ties, like those in the European Union, have made war in Europe very costly and unlikely.

Waltz’s idea that most countries can safely manage nuclear weapons is criticized by some scholars. They say he underestimates long-standing conflicts and the risk that weak countries might not protect nuclear materials from being stolen or used by terrorist groups.

A TV show called Doomsday: On The Brink showed many accidents involving U.S. and Soviet nuclear weapons over 40 years. Even after the Cold War, events like the 1995 Norwegian rocket incident showed that mistakes could still lead to nuclear risks. Experts warn that future leaders or military officials might try to use nuclear weapons for political reasons, and that human nature could drive people to seek power through weapons of mass destruction.

Professor Scott Sagan wrote that when one country gets nuclear weapons, others may follow to balance power or protect themselves. He called this the "proliferation begets proliferation" effect. For example, after the United States used nuclear weapons in World War II, the Soviet Union started its own program. This led France and the United Kingdom to also develop nuclear weapons.

Sagan also noted that a country’s economy affects whether it can successfully build nuclear weapons. A study by Dong-Jong Joo and Erik Gartzke explained that wealthier countries are more likely to succeed in creating nuclear weapons.

Former Iranian President Mahmoud Ahmadinejad often criticized the idea of "nuclear apartheid," which refers to a system where only some countries have nuclear weapons.

Artificial intelligence

Since 2023, there have been concerns that the common use of large language models (LLMs) might help people learn about nuclear weapons for harmful purposes like terrorism or spying. In 2024, the company Anthropic, which created the public LLM called Claude, began working with the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy. Their goal was to develop filters to identify nuclear technology-related questions. These filters were meant to be shared with the Frontier Model Forum, a group that includes major AI companies such as Amazon, Google, OpenAI, Meta, and Microsoft. The filters can tell the difference between questions about nuclear weapons and similar questions about civilian nuclear power. The NNSA tested the filters for one year, and the results showed the filters correctly identified 94.8% of harmful conversations, missed 5.2% of harmful conversations, and never incorrectly labeled a harmless conversation as harmful. Large language models, which learn from large sets of human-written text, may not always give accurate answers about physics. In March 2025, it was reported that Nvidia was creating a "world model," which is different from LLMs and is trained using physical data instead of text.