July 16, 1945: World’s first test of a nuclear device is conducted by exploding a bomb on a tower at Trinity site, Alamogordo, N.M.
August 6, 1945: First atomic bomb is dropped on Hiroshima; three days later a second atomic bomb is dropped on Nagasaki.
1947: General Dwight D. Eisenhower orders an effort to monitor the nuclear tests of other countries.
August 29, 1949: The U.S.S.R. becomes the second nation in the world to test a nuclear device (also in the atmosphere).
September 3, 1949: The Soviet explosion is detected by an American plane that collects radioactive debris in the upper atmosphere. It is the first nuclear explosion monitored by a country other than the testing power.
October 3, 1952: The U.K. becomes the third nuclear weapons state, when it explodes its first nuclear device (also in the air).
Mid-1950s: Many national and international groups bring public attention to the genetic hazards of radioactive materials produced by the continuing nuclear testing.
September 19, 1957: First underground nuclear test explosion is conducted at the Nevada test site.
February 13, 1960: France tests its first nuclear device.
October 31, 1961: The Soviet Union explodes the largest device ever tested, the “Big John,” with a yield of more than 50 megatons. It was promptly detected all around the world.
August 5, 1963: Limited Test Ban Treaty is signed by the U.K., the U.S. and the U.S.S.R., banning testing in the atmosphere, underwater and in space. China and France refuse
October 16, 1964: China tests its first nuclear device, becoming the fifth nation to do so.
July 1, 1968: Sixty-one countries sign the Non-Proliferation Treaty, prohibiting the transfer of nuclear weapons technology to nonnuclear weapons states. India, Israel, North Korea and Pakistan refuse to sign.
May 18, 1974: India tests its first nuclear device (underground).
1992: The U.S. under President George H. W. Bush declares a moratorium on all nuclear testing.
September 10, 1996: The United Nations General Assembly votes in favor of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which prohibits all nuclear test explosions.
September 24, 1996: President Bill Clinton signs the CTBT for the U.S. By the end of that day 66 nations, including the four other nuclear weapons states (China, France, Russia and the U.K.) sign the treaty. India, North Korea and Pakistan do not sign.
May 11 and 13, 1998: India conducts two sets of underground nuclear tests, breaking a de facto global moratorium on testing that had prevailed since the CTBT was opened for signatures in 1996.
May 28, 1998: In response to India’s renewed testing, Pakistan conducts two sets of its own underground nuclear tests.
October 13, 1999: U.S. Senate votes to withhold its advice and consent to the CTBT.
2001: Shortly after taking office, President George W. Bush declares the CTBT is not in U.S. interests. He continues the U.S. moratorium on testing.
October 9, 2006: North Korea tests its first nuclear device (underground).
December 31, 2008: 180 countries have signed the CTBT, including 41 of 44 countries that must sign it before it can go into force. Only India, North Korea and Pakistan remain holdouts.