1945 Manhattan Project: the Atomic Age begins when the United States successfully detonates a plutonium-based test nuclear weapon at the Trinity site near Alamogordo, New Mexico.
1945 World War II: Hiroshima is devastated when the atomic bomb "Little Boy" is dropped by the United States B-29 ''Enola Gay''. Around 70,000 people are killed instantly, and some tens of thousands die in subsequent years from burns and radiation poisoning.
1945 World War II: Nagasaki is devastated when an atomic bomb, ''Fat Man'', is dropped by the United States B-29 ''Bockscar''. 39,000 people are killed outright.
1945 The USSR's nuclear program receives plans for the United States plutonium bomb from Klaus Fuchs at the Los Alamos National Laboratory.
1952 The United Kingdom successfully tests a nuclear weapon.
1953 Cold War: U.S. President Dwight D. Eisenhower formally approves the top secret document National Security Council Paper No. 162/2, which states that the United States' arsenal of nuclear weapons must be maintained and expanded to counter the communist threat.
1955 Eighteen Nobel laureates sign the Mainau Declaration against nuclear weapons, later co-signed by thirty-four others.
1962 Cuban Missile Crisis: US President John F. Kennedy, after internal counsel from Dwight D. Eisenhower, announces that American reconnaissance planes have discovered Soviet nuclear weapons in Cuba, and that he has ordered a naval "quarantine" of the Communist nation.
1967 More than sixty nations sign the Outer Space Treaty banning nuclear weapons in space.
1971 Eighty-seven countries, including the US, UK, and USSR, sign the Seabed Treaty outlawing nuclear weapons in international waters.
1974 Nuclear test: under project Smiling Buddha, India successfully detonates its first nuclear weapon becoming the sixth nation to do so.
1979 Nuclear false alarm: the NORAD computers and the Alternate National Military Command Center in Fort Ritchie, Maryland detected purported massive Soviet nuclear strike. After reviewing the raw data from satellites and checking the early warning radars, the alert is cancelled.
1981 Cold War: In Geneva, representatives from the United States and the Soviet Union begin to negotiate intermediate-range nuclear weapon reductions in Europe (the meetings ended inconclusively on December 17).
1985 U.S.S.R performs nuclear test at Eastern Kazakhstan/Semipalatinsk. thumb
1992 Boris Yeltsin announces that Russia will stop targeting United States cities with nuclear weapons.
1994 Sino-Soviet Split: Russia and the People's Republic of China agree to de-target their nuclear weapons against each other.
1994 North Korea nuclear weapons program: North Korea and the United States sign an agreement that requires North Korea to stop its nuclear weapons program and agree to inspections.
1995 The Norwegian Rocket Incident: Russia almost launches a nuclear attack after it mistakes Black Brant XII, a Norwegian research rocket, for a US Trident missile.