The Second World War ends in Europe on 7 May 1945 when Germany surrenders unconditionally. In the Pacific, fighting continues until the United States drops atomic bombs on Hiroshima and Nagasaki on 6 and 9 August 1945 respectively, killing about 120,000 people outright and fatally injuring over 100,000 more.
Japanese Emperor Hirohito surrenders unconditionally on 15 August 1945.
Following the war, Eastern European countries occupied by the Soviets are turned into "satellite states" governed by "puppet" communist regimes. The 'Iron Curtain' falls across Europe and a 'Cold War' develops between the USSR and the West.
The Cold War intensifies on 29 August 1949 when the USSR explodes an atomic weapon of its own. An "arms race" then begins between the US and USSR, with both sides developing huge arsenals of thermonuclear (hydrogen) bombs and Inter-Continental Ballistic Missiles (ICBMs) capable of delivering nuclear warheads across continents.
An uneasy and dangerous balance of deterrence is established under the principle of 'Mutually Assured Destruction' (MAD).
Born on 21 May 1921 in Moscow, the capital of the USSR, into a cultured and liberal family belonging to the Moscow intelligentsia. His father is a physics teacher. Sakharov receives his initial education at home, not entering public school until the age of 13.
1938 - A gifted student, Sakharov enrols at the faculty of physics at Moscow University immediately after completing his schooling.
1941 - Germany invades the USSR on 22 June, bringing the Soviets into the war. Sakharov, who is classified as medically unfit for military service, is evacuated to Ashkhabad in Central Asia to complete his studies.
1942 - Sakharov receives his degree in physics, passing his finals with distinction. In September he is assigned to work as an engineer and inventor at a large munitions factory on the Volga River, staying in the post until 1945.
While working at the munitions factory be meets Klavdia Vikhireva, a laboratory technician. The couple marry in 1943.
1945 - With the war over, Sakharov returns to Moscow and begins graduate studies at the Lebedev Institute, the Department of Physics in the Academy of Sciences of the USSR. His chosen area of research is nuclear physics.
1948 - After receiving his doctorate for work on particle physics, Sakharov joins a group of research scientists working on the USSR's top-secret nuclear weapons project, an area in which he will be employed for the next 20 years. He will be a key figure in the development of the Soviet hydrogen bomb.
Sakharov will later say, "At the time we were all convinced that this work was of vital significance for the balance of power in the world and we were fascinated by the grandeur of the task."
"I understood, of course, the terrifying, inhuman nature of the weapons we were building," he says, "But the recent war had also been an exercise in barbarity; and although I hadn't fought in that conflict, I regarded myself as a soldier in this new scientific war."
1949 - The USSR explodes its first atomic bomb at Semipalatinsk in eastern Kazakhstan on 29 August.
1950 - Sakharov moves to the 'Installation', a secret facility in the central Volga region of the USSR dedicated to the design of nuclear weapons. He will work there with other team members to develop his 'Sloyka' design concept for a hydrogen bomb.
1952 - Great Britain enters the nuclear race on 3 October when it explodes an atomic bomb at the Montebello Islands, off the northwest coast of Western Australia.
The US successfully detonates a hydrogen bomb at Eniwetok Atoll (the Marshall Islands) on 1 November. Though smaller in size than the bombs exploded over Hiroshima and Nagasaki, the hydrogen bomb is 2500 times more powerful. The island on which the bomb is tested is completed destroyed.
1953 - The USSR conducts its first successful test of a prototype hydrogen bomb on 12 August. The bomb has been produced using the 'Sloyka' design suggested by Sakharov. His research will also provide key contributions to the detonation of the USSR's first full-fledged hydrogen bomb on 22 November 1955 and to the 'Czar Bomb' of 1961, the most powerful device ever exploded on Earth.
Sakharov begins to consider the "moral problems inherent in (his) work"; a process of growing unease that will take him to a point where he feels compelled to make his views public.
At the same time, he is elected to the Russian Academy of Science, becoming its youngest member. He will also be awarded the Order of Lenin two times, the Stalin Prize once, and the Hero of Socialist Labour Medal three times.
1957 - Sakharov, having reached the point where he feels personally responsible for "the problem of radioactive contamination from nuclear explosions", starts to set out his views in scientific papers such as 'Radioactive Carbon from Nuclear Explosions and Nonthreshold Biological Effects' and 'The Radioactive Danger of Nuclear Tests'.
He also writes letters to the Soviet authorities, including Nikita Khrushchev, first secretary of the Communist Party, arguing that atmospheric nuclear tests should be stopped and that the USSR should accept a proposal by the US for a limited ban on tests.
Meanwhile, Great Britain explodes a hydrogen bomb at Christmas (Kiritimati) Island in the Pacific Ocean on 8 November.
1960 - France conducts its first test of an atomic bomb on 13 February, exploding the device at Reggane in Algeria. France will successfully detonate a hydrogen bomb on 24 August 1968.
1962 - On 25 September Sakharov phones Khrushchev asking him to stop an atmospheric test of a nuclear weapon planned for the following day. Though Khrushchev assures Sakharov that he will inquire about postponing the test, the bomb is detonated as planned.
"After that," Sakharov later says, "I felt myself another man. I broke with my surroundings. I understood there was no point arguing."
1963 - At negotiations held in Moscow in July the USSR, the US and Great Britain sign a treaty banning nuclear tests in the atmosphere, in space, and in the ocean. Underground tests are allowed to continue. The treaty is signed on 5 August and comes into effect on 10 October.
"I consider the Moscow Treaty of historic significance," Sakharov later says. "It has saved the lives of hundreds of thousands, possibly millions, of people who would have perished had testing continued. And perhaps even more important, the treaty was a step toward reducing the risk of thermonuclear war. I am proud of my contribution to the Moscow Treaty."
1964 - Together with 24 other prominent intellectuals and artists, Sakharov writes to First Secretary Leonid Brezhnev, warning him against the rehabilitation of the dead and disgraced Soviet dictator Joseph Stalin, saying that "people would never understand or accept" Stalin's restoration to a place of honour.
The Chinese explode an atomic bomb at Lop Nor in the Xinjiang Uygur Autonomous Region on 16 October. They will conduct their first successful test of a hydrogen bomb on 17 June 1967.
1967 - Sakharov sends a secret memorandum to the Soviet leadership advising them to accept a US proposal for a moratorium on the development of anti-ballistic missile defence systems, arguing that not to do so would only lead to a further intensification of the arms race and increase the likelihood of nuclear war.
When his suggestion that his concerns be made public is rejected by the leadership, he decides to act by himself.
1968 - Sakharov distils his concerns into 'Reflections on Progress, Peaceful Coexistence and Intellectual Freedom', an essay arguing that the total annihilation of civilisation that would result from a nuclear war can only be averted by worldwide cooperation transcending national and ideological boundaries.
The essay presents two theses:
"1. The division of mankind threatens it with destruction. ... Only universal cooperation under conditions of intellectual freedom and the lofty moral ideals of socialism and labour, accompanied by the elimination of dogmatism and pressure of the concealed interests of ruling classes, will preserve civilisation. ...
"2. The second basic thesis is that intellectual freedom is essential to human society - freedom to obtain and distribute information, freedom for open-minded and unfearing debate, and freedom from pressure by officialdom and prejudices. Such a trinity of freedom of thought is the only guarantee against an infection of people by mass myths, which, in the hands of treacherous hypocrites and demagogues, can be transformed into bloody dictatorship. Freedom of thought is the only guarantee of the feasibility of a scientific democratic approach to politics, economics and culture."
Circulated as 'Samizdat' (self-printed, typewritten copies), the essay quickly becomes known throughout the USSR. Although the essay receives no official acknowledgement, the Soviet Government agrees to begin negotiations with the US on an anti-ballistic missile treaty.
Following the publication of the essay by the Dutch newspaper 'Het Porool' and 'The New York Times' in July, Sakharov is dismissed from the nuclear weapons program and stripped of the privileges granted to those at the top of the Soviet system.
Meanwhile, the USSR, the US, Britain, France and China agree to sign the Nuclear Nonproliferation Treaty, pledging to restrict the development, deployment, and testing of nuclear weapons.
The USSR and US also initiate the Strategic Arms Limitation Talks (SALT).
1969 - In March Sakharov's wife Klavdia dies of cancer, leaving him with three children, aged 24, 19, and 11 years. Sakharov returns to the Lebedev Institute in May, where he begins to investigate problems connected with the theory of elementary particles, the theory of gravitation, and cosmology.
1970 - The defence of human rights and of victims of political trials become central concerns for Sakharov, who helps to found and run the Committee for Human Rights. Working in the human rights milieu, Sakharov meets Elena Bonner. The couple marry in 1972.
1972 - The SALT negotiations between the USSR and the US result in the Anti-Ballistic Missile Treaty and the Interim Agreement on the Limitation of Strategic Offensive Arms. Further SALT negotiations will lead to a treaty limiting the total number of USSR and US missile launchers.
1973 - Sakharov's rising profile as a champion of human rights results in an increase in the pressure being applied against him and his wife by the Soviet regime through the official press. In February 1973 the journal 'Literaturnaya Gazeta' prints the first official public criticism of Sakharov.
During the year the International League for Human Rights presents Sakharov with its Human Rights Award. In 1976 he will be elected an honorary vice president of the league.
1974 - India joins the nuclear weapons club when it explodes an atomic bomb in Rajasthan on 18 May.
Meanwhile, in an article published on 24 August, Sakharov predicts the development of the World Wide Web, almost 20 years before it first appears.
"Far in the future, more than 50 years from now, I foresee a universal information system (UIS), which will give everyone access at any given moment to the contents of any book that has ever been published or any magazine or any fact," he writes.
"The UIS will have individual miniature-computer terminals, central control points for the flood of information, and communication channels incorporating thousands of artificial communications from satellites, cables, and laser lines. Even the partial realisation of the UIS will profoundly affect every person, his leisure activities, and his intellectual and artistic development. Unlike television ... the UIS will give each person maximum freedom of choice and will require individual activity. But the true historic role of the UIS will be to break down the barriers to the exchange of information among countries and people."
1975 - Sakharov is awarded the Nobel Peace Prize for his "fearless personal commitment in upholding the fundamental principles for peace between men", sparking an intensification of the official vilification campaign. Sakharov, who is the first Soviet citizen to receive the peace prize, is labelled "a Judas" and "laboratory rat of the West" by the Soviet authorities and prevented from travelling to Oslo to receive the award. His wife, Elena Bonner, accepts it on his behalf.
The Nobel Committee's citation states that Sakharov "is a powerful inspiration for all true work for peace."
"Uncompromisingly and with unflagging strength Sakharov has fought against the abuse of power and all forms of violation of human dignity, and he has fought no less courageously for the idea of government based on the rule of law," the Committee says.
In his acceptance speech, which is read by his wife, Sakharov says, "To keep one's self-respect, one must ... act in accordance with the general human longing for peace, for true détente, for genuine disarmament.
"This is the reason why I am so deeply moved by your appreciation of my activity as a contribution to peace. But what made me particularly happy was to see that the Committee's decision stressed the link between defence of peace and defence of human rights, emphasising that the defence of human rights guarantees a solid ground for genuine long-term international cooperation."
Sakharov's Nobel lecture, 'Peace, Progress, Human Rights', is presented by his wife on 11 December.
"In struggling to protect human rights we must, I am convinced, first and foremost act as protectors of the innocent victims of regimes installed in various countries, without demanding the destruction or total condemnation of these regimes," the prepared text says.
"We need reform, not revolution. We need a pliant, pluralist, tolerant community, which selectively and tentatively can bring about a free, undogmatic use of the experiences of all social systems. What is détente? What is rapprochement? We are concerned not with words, but with a willingness to create a better and more friendly society, a better world order."
1979 - Sakharov publicly denounces the USSR's December invasion of Afghanistan, stirring the authorities to act.
1980 - On 22 January he is detained, stripped of all his official Soviet awards, and exiled to Gorky (now called Nizhni Novgorod), 400 km east of Moscow. He will remain in exile for almost seven years, though he is never charged, tried, or convicted of any crime.
Sakharov later describes the terms of his exile: "Overt surveillance, prohibition against leaving the city limits, prohibition against meeting with foreigners and 'criminal elements', prohibition against correspondence and telephone conversations with foreigners, including scientific and purely personal communications, even with my children and grandchildren. I was instructed to report three times a month to the police, and threatened that I would be taken there by force if I failed to obey."
However, while isolated from friends and colleagues he is still able to communicate with the outside world via his wife, who ensures that his writings are published in the USSR and abroad.
Sakharov also uses the time to write the first part of his 'Memoirs', though he is forced to rewrite it from memory when the KGB (Komitet Gosudarstvenoi Bezopasnosti - the Soviet secret police force) steals the manuscript.
1981 - Sakharov and his wife go on a hunger strike together to protest the refusal by the Soviet authorities to grant their daughter-in-law permission to travel to the US to join her husband, Bonner's son. Sakharov is forcibly hospitalised and denied any contact with his wife. His daughter-in-law is, however, allowed to join her husband.
1983 - Sakharov's essay 'The Danger of Thermonuclear War' is published.
1984 - His wife, Elena Bonner, is also exiled to Gorky. Bonner is suffering from a heart condition but is denied adequate medical treatment. Sakharov resorts to hunger strikes to force the authorities to allow her to travel to the West for treatment but is again forcibly hospitalised and denied further contact with Bonner.
In the US, President Ronald Reagan launches the Strategic Defence Initiative, also known as 'Star Wars'. Sakharov opposes the initiative, arguing that like the earlier anti-ballistic missile defence systems proposal, it would increase the likelihood of nuclear war.
1985 - Mikhail Gorbachev comes to power in the USSR and begins a program of social reform called 'Perestroika' (reconstruction).
Bonner is finally granted permission to travel to the US for heart surgery, although when she returns she is again placed in exile with her husband.
1986 - The estimated world arsenal of nuclear warheads has reached 40,000 - the equivalent of one million Hiroshima bombs. Long-held suspicions that Israel has a well-developed nuclear weapons program are confirmed in September when Mordecai Vanunu, an Israeli arms technician, provides hard evidence of an underground bomb factory.
On 16 December Gorbachev invites Sakharov to return to Moscow and perform "patriotic work", ending his and Bonner's period of exile.
Sakharov is elected to the Presidium of the Academy of Science and as a member of the Congress of People's Deputies (the Soviet parliament), where he becomes joint leader of the democratic opposition faction. He is also appointed as a member of the government commission set up to draft a new Soviet constitution and serves as a national ombudsman.
1987 - In December Gorbachev and US President Ronald Reagan sign the Intermediate Range Nuclear Forces Treaty, which calls for the removal of many nuclear armed ballistic missiles deployed in Europe and the USSR and the destruction of all Soviet and US missiles with ranges of about 500 to 5500 km.
1988 - The European Parliament inaugurates the annual Sakharov Prize for Freedom of Thought. The prize seeks "in the spirit of Andrei Sakharov ... to honour individuals or organisations who have devoted themselves to the defence of human rights and fundamental freedoms and the struggle against oppression and injustice."
1989 - Sakharov becomes critical of Gorbachev, insisting that the Perestroika reforms should go much further. In June, at the First Congress of People's Deputies, he appeals for a radical reformation of the Soviet system including the repeal of the clause in the constitution giving the Communist Party a monopoly on political power.
In December he completes a draft of a new constitution for the 'Union of Soviet Republics of Europe and Asia'.
Sakharov dies of a heart attack in Moscow on 14 December.
1990 - The Communist Party gives up its constitutional hold over the Soviet political system, as demanded by Sakharov in 1989.
1995 - Nuclear powers agree to the Negative Security Assurances, pledging to never use nuclear weapons against nations that do not possess them. The following year the Comprehensive Test Ban Treaty is introduced, although the US refuses to ratify it.
France, meanwhile, begins underground nuclear tests at Mururoa Atoll in the South Pacific.
1998 - Pakistan confirms its possession of nuclear weapons in May when it conducts test explosions in the Chagal Hills in Baluchistan.
2001 - The US withdraws from the Anti-Ballistic Missile Treaty.
2002 - In May US President George W. Bush and Russian President Vladimir Putin sign the Treaty of Moscow (also know as SORT) setting the maximum number of deployed strategic nuclear weapons that will remain in the US and Russian arsenals by 2012 at 1700-2200.
2003 - The Centre for Defence Information estimates that as at February 2003 there were about 30,000 intact nuclear warheads throughout the world. About 28,800 were retained by the US and Russia, with 17,500 being considered operational. The centre estimates that over 128,000 nuclear warheads have been built worldwide since 1945. About 55% of these had been constructed by the US, and about 43% by the USSR/Russia. According to the centre, the US spent US$3.5 trillion between 1940 and 1995 on preparations for a nuclear war.
The 2002 Bulletin of Atomic Scientists estimates that Russia possesses 8,600 nuclear warheads, the US 8,000, China 400, France 350, Britain 200, Israel 200, Pakistan 48, and India 35.
A later estimate by Jeffrey Lewis, research fellow at the Centre for International and Security Studies at the University of Maryland School of Public Policy, places the number of operationally deployed nuclear weapons held by China at between 80 and 130.
In April Elena Bonner objects to a plan to erect a statue honouring Sakharov in Pushkin Square in central Moscow. "What is Russia today?" she asks, "It is a country in which a third of its population lives below the poverty line ... a country waging bloody war in Chechnya ... a country where nearly every day free mass media are being destroyed by political or financial pressure. ... Such a Russia does not correspond with the idea of a monument to Sakharov."
The Moscow authorities decide to go ahead with the statue despite Bonner's objections.
On 5 May another statue of Sakharov is unveiled in St Petersburg. The statue is situated in a square named after Sakharov in 1996.
Reflecting on the nuclear arms race in his 'Memoirs', Sakharov wrote:
"Have Soviet and American atomic scientists helped to keep the peace? After more than 40 years, we have had no third world war, and the balance of nuclear terror ... may have helped to prevent one. But I am not at all sure of this; back then, in those long-gone years, the question didn't even arise. What most troubles me now is the instability of the balance, the extreme peril of the current situation, the appalling waste of the arms race. ... Each of us has a responsibility to think about this in global terms, with tolerance, trust, and candour, free from ideological dogmatism, parochial interests, or national egotism."
While the threat of a global nuclear conflict may have subsided following the end of the Cold War, the danger of the "limited" use of nuclear arms by nation states or terrorist groups remains. The US, Russia, Great Britain, France, China, India, Pakistan and Israel all possess nuclear weapons. North Korea is thought to have the capacity to build and deliver nuclear arms and may already have built a handful of bombs. Algeria, Argentina, Brazil, Iran, Iraq and Libya, South Africa and Taiwan have all at some stage been identified as having nuclear weapons ambitions.
The genie unleashed by Sakharov and the other pioneering nuclear scientists may never be put back into the bottle. If it is it will require the dedication of scientists like Sakharov - people prepared to recognise that their research does not occur in a vacuum and that there are moral imperatives that should take precedence over scientific inquiry, even if this requires some personal sacrifice.