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Manhattan Project Begins
Manhattan Project officially begins. This secret US project that leads to the development of the first atomic bomb. -
"Atomic Age" Begins
The “Atomic Age” begins. The first-ever nuclear weapons test, codenamed the Trinity Test, is carried out by the United States at the White Sands Proving Ground in New Mexico. This implosion-design device is called “The Gadget.” -
Hiroshima Bombing
First atomic bomb to be used as a weapon, known as “Little Boy” (a uranium based device), is dropped over Hiroshima during World War II. -
Nagasaki Bombing
Three days after the first nuclear weapon was dropped on Hiroshima, “Fat Man,” an implosion-device similar to “The Gadget” weapon tested in New Mexico, is dropped over Nagasaki. -
First Soviet Nuclear Weapon Test
Soviet Union conducts its first nuclear weapon test known as “RDS-1” at the Semipalatinsk test site in Kazakhstan. -
UK First Nuclear Test
United Kingdom conducts its first nuclear weapon test known as Operation Hurricane at the Montebello Islands off the coast of Western Australia. -
"Mike" Test
First hydrogen bomb test, codenamed “Mike,” carried out by the United States at the Enewetak atoll in the Marshall Islands. -
Castle Bravo test
The first hydronuclear weapon test, codenamed Castle Bravo, is carried out by the United States. The yield was 15 megatons, making it the most powerful weapon ever tested by the United States. -
IAEA Established
The International Atomic Energy Agency is established to promote peaceful uses of the atom and verify non-diversion of material to weapons purposes. -
France First Nuclear Weapon Test
France conducts its first nuclear weapon test, called "Gerboise bleue," in Algeria. -
The 'Tsar Bomba" Tested
USSR conducts the most powerful nuclear weapon test ever. The yield of the "Tsar Bomba" was 50 megatons; 1,400 times more powerful than the two bombs used in World War II over Hiroshima and Nagasaki. -
Partial Test Ban Treaty inf orce
Partial Nuclear Test Ban Treaty (also known as the Limited Test Ban Treaty) enters into force. It prohibits nuclear testing in the atmosphere, in outer space, and under water. -
China Tests First Nuclear Weapon
China conducts its first nuclear weapon test codenamed “596” at the Lop Nur test site. -
NPT Opens for Signature
The Treaty on the Non-Proliferation of Nuclear Weapons, also known as the Nuclear Non-Proliferation Treaty (NPT), opens for signature. Read more on UN Office for Disarmament Affairs -
Treaty of Tlatelolco in force
The Treaty of Tlatelolco, the first nuclear-weapon-free zone (NWFZ), covering Latin America and the Caribbean, provisionally enters into force. -
NPT Enters Into Force
Nuclear Non-Proliferation Treaty (NPT), enters into force. It becomes known as the "cornerstone" of international security. Treaty Text -
SALT I Negotiations
The United States and Soviet Union hold Strategic Arms Limitation Talks (SALT) from November 17, 1969 to May 26, 1972, aimed at limiting missile systems and other strategic armaments. The ABM Treaty was also negotiated as a result of these meetings. -
ABM Treaty in force
The Treaty between the United States and Soviet Union on the Limitation of Anti-Missile Ballistic Systems (ABM Treaty) enters into force. The Treaty obligated the parties to limit their deployed ABM systems to no more than two sites, with 100 ABM launchers and 100 interceptor missiles each. -
India's PNE
India conducts a "peaceful nuclear explosion" codenamed the Smiling Buddha. -
Threshold Test Ban Treaty Signed
The Treaty on the Limitation of Underground Nuclear Weapon Tests, also known as the Threshold Test Ban Treaty, is signed by the United States and the Soviet Union. This treaty prohibited underground nuclear tests above the yield of 150 kilotons. -
First NPT Review Conference starts
The First NPT Review Conference takes place. The number of states parties is 91. The conference decides to hold review conferences every five years thereafter to review the implementation of the NPT. The Final Document reaffirms commitment to treaty objectives and urges nuclear weapon states to comply with disarmament obligations.1975 Final Declaration, Complete Final Document: Part I - Organization and Work of the Conference -
NSG meets for the first time
In November 1975, the Nuclear Suppliers Group meets for the first time in London. Created in response to India's nuclear test, the group is focused on improving export controls to prevent proliferation of nuclear weapons and related technology -
SALT II Negotiations
U.S. and USSR sign the SALT II Treaty but never ratify the agreement due to the Soviet invasion of Afghanistan later that year. -
Second NPT RevCon starts
The second NPT Review Conference convenes. The number of states parties is 112. The Review Conference fails to reach consensus on a Final Document. Many non-nuclear weapon states call on the United States and USSR to ratify the SALT II Treaty, but the United States had withdrawn from the negotiations due to the Soviet invasion of Afghanistan. Read more on Reaching Critical Will. -
Third NPT Review Conference starts
27 August - 21 September 1985, the third NPT Review Conference is held in Geneva. Parties to the treaty now number 131. Although a majority of the parties praises the NPT as a success, some argue that horizontal proliferation, particularly in Israel and South Africa, is threatening the treaty's objective of preventing the spread of nuclear weapons. The conference adopts the Final Document urging expansion of nuclear-weapon-free-zones and progress on nuclear disarmament. Read more -
The Chernobyl disaster
An accident at the Chernobyl Nuclear Power Plant in Ukraine, the worst such accident in history, results in the releae of large amounts of radiation that spreads over Belarus,Ukraine, and other European countries, in USSR and abroad. -
Reykjavik Summit
At a summit meeting in Reykjavik, Iceland, U.S. President Ronald Reagan and Soviet General Secretary Mikhail Gorbachev discuss limiting U.S. and Soviet nuclear arsenals. The meeting fails to produce a concrete agreement as the Soviet Union demands that the United States first cancel plans for the Strategic Defense Initiative (SDI), which the United States refused to do. -
Treaty of Rarotonga in force
The Treaty of Rarotonga, a nuclear-weapon-free zone covering the South Pacific, enters into force. -
INF Treaty in force
The Treaty between the United States of America and the Soviet Union on the Elimination of their Intermediate-range and Shorter-range Missiles (INF Treaty) enters into force. -
Berlin Wall falls
In November 1989, Berlin Wall falls, marking the end of the Cold War and, with it, the end of the superpowers’ nuclear arms race. -
Fourth Review Conference
On 20 August-14 September1990, the Fourth NPT Review Conference takes place in Geneva. There are 140 States parties to the Treaty. The RevCon failed to adopt a final declaration due to lack of progress on disarmament and negotiation of a comprehensive nuclear test ban, along with disagreements over negative security assurances being provided to non-nuclear-weapon states. Read More on Reaching Critical Will -
South Africa joins NPT
19 July 1991 – South Africa joins the NPT as a non-nuclear-weapon state, after dismantling its secret nuclear weapons program. South Africa is the only country that had manufactured nuclear weapons and voluntarily dismantled them. -
START Treaty Signed
The Treaty Between the United States of America and the Soviet Union (later Russian Federation) on Further Reduction and Limitation of Strategic Offensive Arms (START I) is signed. The treaty established an extensive bilateral verification regime and was expected to cut strategic nuclear arsenals by about 35%. -
Semipalatinsk Site Closed
Semipalatinsk Test Site closes. Kazakhstan’s President Nazarbayev orders the closure of the Semipalatinsk nuclear test site, exactly 42 years after the first Soviet test there. -
China joins NPT
After two decades outside the regime, China accedes to the NPT as a nuclear-weapon state. -
France joins NPT
France accedes to the NPT, the last "official" nuclear-weapon state to do so. -
DPRK leaving NPT
North Korea announces its withdrawal from the NPT, citing “supreme national security interest” under Article X of the Treaty -
DPRK re-joins NPT
North Korea announces a “suspension” of its withdrawal from the NPT one day before it goes into full effect. The decision comes as a result of negotiations with the United States. -
DPRK leaves IAEA
North Korea announces its “immediate withdrawal” from the IAEA -
START I in force
START I enters into force, upon the exchange of instruments of ratification among the United States, Russia, Belarus, Kazakhstan, and Ukraine. The latter three give up nuclear weapons inherited from the Soviet Union. -
NPT Review and Extension Conference Starts
States parties to the NPT convene in New York for the Treaty’s Review and Extension conference. This was the first post-Cold War conference; China and France had recently joined the treaty as NWS; “nuclear roll-back” states South Africa, Belarus, Kazakhstan, Ukraine, Brazil, Argentina are also new members of the NPT. The state parties failed to reach a consensus on the final declaration; but agreed to extend the treaty indefinitely under Article X of NPT. See the Final Documents. Read More. -
NPT Extended Indefinitely
The NPT is extended indefinitely. The package of decisions includes, along with treaty extension, strengthening the review process, Principles and Objectives for Nuclear Disarmament and Nonproliferation, and a Resolution on the Middle East. Read the three Decisions and the Resolution. -
The CTBT Opens for Signature
The Comprehensive Nuclear Test Ban Treaty opens for signature. To enter into force, the Treaty must be ratified by the 44 states listed in its Annex 2, including the five “official” nuclear-weapon states and nuclear weapons possessors outside the NPT. Read More. -
Treaty of Bangkok in force
The Treaty of Bangkok, a nuclear-weapon-free zone covering Southeast Asia, enters into force. -
Additional Protocol approved
The IAEA Board of Governors approves the Model Additional Protocol, a protocol that could be added to existing comprehensive safeguards agreements, providing the IAEA with strengthened safeguards verification authority. Read more about the Additional Protocol -
India's Nuclear Weapons Tests
11-13 May, India carries out a series of nuclear weapon tests known as Pokharan II. -
Pakistan's First NW Test
28-30 May, Pakistan carries out a series of nuclear weapon tests known as Chagai I and II. -
Mongolian NWFZ Recognized
The United Nations officially recognizes Mongolia's nuclear-weapon-free status. -
2000 NPT RevCon concludes
On 24 April - 19 May, NPT member states convene for the Treaty’s sixth Review Conference. States Parties adopt by consensus a Final Document that includes 13 “practical steps for the systematic and progressive efforts to implement Article VI of the Treaty,” which specifically deals with nuclear disarmament. Read more.
Final Document Part I (substantive review; includes the 13 practical steps) -
U.S. leaving ABM Treaty
U.S. President George W. Bush notifies the Russian Federation that the U.S. would be withdrawing from the ABM Treaty. The withdrawal clause in the treaty required a 6 month notification prior to leaving. -
ABM and START II Treaties defunct
US withdrawal from the ABM Treaty takes effect. Russia declares START II defunct on the same day. -
Treaty of Tlatelolco in full force
The Treaty of Tlatelolco, the Latin American NWFZ, enters into full force after Cuba becomes the last state to ratify it. -
DPRK leaves NPT - again
North Korea announces withdrawal from the NPT. -
SORT Treaty in force
The Treaty Between the United States of America and the Russian Federation on Strategic Offensive Reductions (SORT), also known as the Moscow Treaty of Moscow, enters into force. -
UNSCR 1540 adopted
UN Security Council unanimously adopts UNSC Resolution 1540 aimed to prevent the acquisition by non-state actors of weapons of mass destruction and related materials. Read more. -
7th NPT RevCon fails
2-27 May 2005, Seventh NPT Review Conference convenes in New York. States disagree on issues of nuclear disarmament and implementation of the 1995 Middle East Resolution. The Conference concludes without a consensus final document. Read More. See Reaching Critical Will -
First DPRK nuclear weapon test
North Korea conducts its first nuclear weapon test. -
Central Asian Nuclear-Weapon-Free Zone in force
Central Asian nuclear-weapon-free zone is the first such zone located entirely in the Northern hemisphere. Three of the "official" five nuclear-weapon-states (France, UK, US) refuse to recognize the zone. -
President Obama's Prague Speech
U.S. President Obama outlines his vision for achieving a world free of nuclear weapons in Prague, Czech Republic. -
Pelindaba Treaty in force
The Pelindaba Treaty, a nuclear-weapon-free zone covering all of Africa, enters into force. -
New START Signed
The Treaty between The United States of America and the Russian Federation on Measures for the Further Reduction and Limitation of Strategic Offensive Arms (New START) opens for signature. -
Nuclear Security Summit
12-13 April, First Nuclear Security Summit takes place in Washington, DC, bringing together leaders of 46 states who pledge to “secure all vulnerable nuclear material in four years.” -
US Discloses Nuclear Weapons Stockpile Numbers
US Nuclear Weapons Stockpile Fact Sheet. The United States, in an effort to promote transparency, releases declassified information about its nuclear stockpile, stating it possessed 5,113 nuclear warheads. -
2010 NPT Review Conference ends
The eighth NPT Review Conference concludes in New York. Consensus Final Document includes a 64-item action plan on nuclear disarmament, nonproliferation, and peaceful uses. The action plan also contains a set of decisions to advance the implementation of the 1995 Resolution on the Middle East. Read more.
Final Document - Volume I (NPT/CONF.2010/50 (Vol. I)) -
New START enters into force
U.S. Senate gives its consent to the treaty on 22 December 2010, and Russian Parliament completes ratification of the New START on 26 January 26 2011. On 22 March, Russia and the United States begin the exchange of data as stipulated by the treaty. -
Fukushima disaster
A 9.0 magnitute earthquake and subsequent tsunami rock Japan, triggering nuclear accidents at the Fukushima Daiichi and Daini nuclear power plants. -
Nuclear Security Summit
The Nuclear Security Summit starts in Seoul, South Korea to assess progress since 2010 and identify further steps that must be taken to ensure that nuclear materials cannot fall into the wrong hands. Read More.
See CNS analysis of the Summit.
