An atomic cloud over Hiroshima as seen from the "Enola Gay" on August 6, 1945.
U.S. Army via Hiroshima Peace Memorial Museum
First Atomic Bombs are Dropped on Hiroshima and Nagasaki

Aiming to end World War II, the United States dropped the first atomic bomb used in combat on Hiroshima, Japan on August 6. The bomb killed more than one hundred thousand people. On August 9, the United States dropped a second atomic bomb on Nagasaki. That bomb killed more than seventy thousand people. Six days later, Emperor Hirohito of Japan announced his country’s surrender. The bombs were produced by the Manhattan Project, a secret research effort launched by the U.S. government in 1942. They remain the only atomic bombs ever used in war.

U.S. President Dwight D. Eisenhower announces the "Atoms for Peace" program in a speech to the United Nations General Assembly on December 8, 1953.
Educational Video Group via YouTube
IAEA is Created

The International Atomic Energy Agency (IAEA) was created with the mission of promoting and overseeing the peaceful use of nuclear technology, such as in power plants. President Dwight Eisenhower’s December 1953 “Atoms for Peace” speech is considered the institution’s origin. He said an international agency was needed to prevent the proliferation of nuclear technology, warning it could result in “the annihilation of the irreplaceable heritage of mankind.”

U.S. President John F. Kennedy gives a televised address about the Cuban Missile Crisis from the White House on October 22, 1962.
U.S. National Archives via YouTube
The Cuban Missile Crisis

On October 15th, a U.S. military plane discovered Soviet nuclear missiles under construction in Cuba, only about 100 miles from the Florida coast. President John F. Kennedy set up a naval quarantine around Cuba and demanded the dismantling of the missiles in his communication with Soviet leader Nikita Khrushchev. After several tense days, Khrushchev agreed to remove the missiles in exchange for a public U.S. guarantee to not attack Cuba. The United States also agreed in secret to remove certain missiles from Turkey. The crisis remains the closest the world has ever come to a nuclear war.

U.S. President Lyndon B. Johnson looks on as Secretary of State Dean Rusk signs the Treaty on the Nonproliferation of Nuclear Weapons on July 1, 1968.
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The Nonproliferation Treaty Opens for Signature

The UN General Assembly had adopted Resolution 2373 in June 1968, endorsing the draft text of the Treaty on the Nonproliferation of Nuclear Weapons (NPT) and opening it up for signatures, starting in July. Under the NPT, countries without nuclear weapons agreed to never obtain such weapons, but they were allowed to use atomic energy peacefully. The five countries with nuclear weapons at the time—the United States, the Soviet Union, the United Kingdom, France, and China—would all go on to sign the treaty, making a commitment to eventually disarm.

An intermediate range ballistic missile on a launcher during a parade in New Delhi on January 26, 2004.
Antônio Milena/Agência Brasil under CC BY 3.0 BR
India Joins the Nuclear Club

India conducted its first nuclear test, code-named “Smiling Buddha,” in the Rajasthan desert in May 1974. Although the country’s government initially denied it, this was the first time a country beyond the original five NPT-recognized nuclear weapon states had tested a nuclear bomb. India’s rival neighbor Pakistan would later test its first nuclear weapon in 1998.

U.S. Secretary of State James Baker, right, and Russian Foreign Minister Andrei Kozyrev sign a protocol to the Strategic Arms Reduction Treaty in Lisbon on May 23, 1992.
Fernando Ricardo/AP
Belarus, Kazakhstan, and Ukraine Give Up Nuclear Weapons

After the fall of the Soviet Union, an international agreement required all nuclear weapons within the territories of Belarus, Kazakhstan, and Ukraine to be destroyed or transferred over to Russia for destruction. The three former Soviet-republics also agreed to join the NPT as nonnuclear weapon states.

The Egyptian UN delegation, lower left, remain quiet as the German delegation seated behind them applaud the agreement reached at the UN Conference on Nuclear Nonproliferation to make the Treaty on the Nonproliferation of Nuclear Weapons permanent at the United Nations on May 11, 1995.
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The 1995 NPT Review Conference

Twenty-seven years after the NPT’s adoption, countries party to the treaty met and agreed to its indefinite extension. This was not a foregone conclusion. Nonnuclear weapon countries, like Egypt, were disappointed with the lack of progress toward nuclear disarmament. In response to these concerns, NPT parties decided to strengthen the treaty review process, convening preparatory conferences two years before each review conference.

A nuclear bomb detonates at the Mururoa atoll, French Polynesia in 1971.
AFP via AP
The Comprehensive Nuclear Test Ban Treaty

After two years of negotiations, the Comprehensive Nuclear Test Ban Treaty (CTBT) opened for signature at the United Nations. The treaty banned nuclear explosions of any kind, including for weapons tests. But the CTBT has not entered into force because not all the required states — including China, India, Pakistan, and the United States — have ratified it. Despite this, most countries with nuclear weapons — including the United Kingdom, the Soviet Union and later Russia, and the United States — have not conducted nuclear tests since the early 1990s.

The flag of the International Atomic Energy Agency (IAEA) flies in front of the Vienna headquarters.
Heinz-Peter Bader/Reuters
The IAEA’s Model Additional Protocol is Introduced

The IAEA’s Board of Governors approved the Model Additional Protocol, a document meant to enhance countries’ safeguards agreements with the IAEA. These allow the agency to monitor whether countries are using nuclear technology for peaceful purposes. This protocol increased the IAEA’s monitoring abilities by giving the agency further access to information and nuclear sites. A major motivation for the protocol’s creation was the discovery after the 1991 Gulf War that Iraq had pursued an undeclared nuclear weapons program despite being subject to IAEA inspections. Though optional, the additional protocols are now implemented in 127 countries.

A missile on a military vehicle during a parade in Pyongyang on July 27, 2013.
Jason Lee/Reuters
North Korea Withdraws from the NPT

North Korea announced its withdrawal from the NPT, saying “We can no longer remain bound to the NPT, allowing the country’s security and the dignity of our nation to be infringed upon.” Months earlier, the United States announced that North Korean officials had admitted to enriching uranium for nuclear weapons. North Korea denied the claim, but then reopened nuclear facilities it had previously shut down and ordered IAEA inspectors out of the country.

A North Korean soldier uses a pair of binoculars to watch the South Korean side in the truce village of Panmunjom in the demilitarised zone separating the two Koreas, about 55 kilometers (31 miles) north of Seoul, on December 22, 2006.
You Sung-Ho/Reuters
North Korea Conducts a Nuclear Test

Almost four years after withdrawing from the NPT, the North Korean government announced that it had successfully conducted a nuclear test. This came just a year after North Korea committed to abandoning nuclear weapons, accepting IAEA inspections, and rejoining the NPT. The broken commitment was part of international negotiations called the Six Party Talks, but they ultimately collapsed in 2009.

U.S. Secretary of State John Kerry talks with Iranian Foreign Minister Mohammad Javad Zarif in Vienna on January 16, 2016, after the International Atomic Energy Agency verified that Iran has met all conditions under the nuclear deal.
Kevin Lamarque/Pool via AP
A Nuclear Agreement with Iran

The United States, China, France, Germany, Russia, the United Kingdom, and the European Union reached a nuclear agreement with Iran in 2015. Although the country had been a party to the NPT since 1970, Iranian nuclear activities were discovered in 2002, leading to years of negotiations, sanctions and IAEA investigations. The United States and its allies believed Iran intended to build a nuclear weapon, despite the country’s denials. This agreement halted escalating tensions over the dispute, by limiting the capabilities of Iran’s nuclear program and subjecting it to international monitoring more strict than ordinary IAEA safeguards, including continuous surveillance of certain facilities. In exchange, the United States and others relaxed sanctions on Iran’s economy. The deal’s provisions begin to expire in 2025.

The History of Nuclear Proliferation