In October 1939, just after the outbreak of World War II in Europe, the President of the United States Franklin D. Roosevelt received a letter from physicist Albert Einstein and his Hungarian colleague Leo Szilard, calling to his attention the prospect that a bomb of unprecedented power could be made by tapping the forces of nuclear fission. The two scientists, who had fled from Europe in order to escape Nazism, feared that Hitler-Germany was already working on the problem. Should the Germans be the first to develop the envisaged "atomic bomb," Hitler would have a weapon at his disposal that would make it possible for him to destroy his enemies and rule the world.

To avoid this nightmare, Einstein and Szilard urged the government of the United States to join the race for the atomic bomb. Roosevelt agreed, and for the next four and half years a vast, utterly secret effort was launched in cooperation with the United Kingdom. Code-named "The Manhattan Project," the effort eventually employed more than 200,000 workers and several thousands scientists and engineers, many of European background. Finally, on July 16, 1945, the first atomic bomb was tested in the midst of the Alamogordo desert in New Mexico. Its power astonished even the men and women who had constructed it. As he witnessed the spectacular explosion, Robert Oppenheimer, the physicist who had directed the scientific work on the bomb, remembered a line from the Vedic religious text Bhagavad-Gita: "I am become death, the shatterer of worlds."

By the time of the Alamogordo test, Germany had already surrendered. This meant that the potential threat of a Nazi atomic bomb no longer existed. But the war in the Pacific was still raging, and the President of the United States Harry S. Truman decided to use the atomic bomb in order to force the Japanese leadership to surrender as quickly as possible. Thus, on August 6 an atomic bomb with an explosive yield equivalent to 12.5 kilotons of the explosives TNT (trinitrotoluene) was dropped on the Japanese city of Hiroshima, instantly killing some 70,000 of its inhabitants, with another 70,000 deaths registered by the end of 1945. Meanwhile, on August 9, a second bomb was used against the city of Nagasaki. This explosion had a higher yield (equivalent to 22 kilotons of TNT) but caused fewer instant deaths. However, many of the survivors suffered from heavy burns, radiation sickness, etc., and the death toll continued to rise. By the end of the year more than 70,000 of Nagasaki's citizens had lost their lives. Five years later, as many as 340,000 people, or 54 percent of the original population, had died from the two explosions.

After the Japanese surrender on August 15, 1945, many people called for a ban on nuclear weapons in order to avoid a nuclear arms race and the risk of future catastrophes like the ones in Hiroshima and Nagasaki. Both the United States and the Soviet Union declared that they were in favor of putting the atomic bomb under foolproof international control. In spite of these declarations, the big powers were, in fact, never ready to give up their own nuclear weapons programs. By the end of 1946 it was clear to everybody that the effort to prevent a nuclear arms race had failed. Indeed, the Soviet Union had already launched a full-speed secret nuclear weapons program in an attempt to catch up with the United States. Thanks in part to espionage, the Soviet scientists were able to build a blueprint of the American fission bomb that was used against Nagasaki and to conduct a successful testing of it on August 29, 1949.

In its turn, the fact that the Soviet Union had become a nuclear power figured heavily when President Truman in early 1950 decided to launch a crash program in order to develop a more advanced type of nuclear weapons, the so-called hydrogen bomb. In contrast to the first atomic bombs, which destructive power came from the process of nuclear fission, the "H-bomb" would use a small fission bomb to trigger a tremendously powerful process of nuclear fusion.

Today eight countries are possessing nuclear weapons. The five nuclear weapons states United States, Russia (former Soviet Union), United Kingdom, France and China, are the only countries allowed to have nuclear weapons according to the Non-Proliferation Treaty (NPT) from 1970. All members of the United Nations except Israel, India and Pakistan have signed the NPT.

By 1954, both the United States and the Soviet Union had successfully tested their first generation of H-bombs. The tests proved that fusion bombs could easily be made to produce explosions more than 1,000 times as powerful as the fission bombs used in the Second World War. The most powerful explosion ever took place at Novaya Zemlya on October 30, 1961, when the Soviet Union tested a "monster bomb" with a yield equivalent to 50 megatons of TNT. It has been estimated that this explosion alone released more destructive power than all bombs and explosives used in the Second World War added together, including the three nuclear explosions of July and August 1945.

By 1961, two more countries had developed and successfully tested nuclear weapons. United Kingdom had started its program during the Second World War in close co-operation with the United States, and the first British bomb was tested on October 3, 1952. On February 13, 1960, France followed suit. The French program received very little technological and scientific support from other countries. Four and a half years later, on October 16, 1964, China became the fifth nuclear power after having received only reluctant assistance from the Soviet Union.

In the early 1960s, many military experts and political leaders feared that the proliferation of nuclear weapons was bound to continue, and that within a decade or two a dozen additional countries were likely to cross the nuclear threshold. In an attempt to forestall such a development, the United States and the Soviet Union took the lead in negotiating an international agreement that would prohibit the further spread of nuclear weapons without banning the utilization of nuclear energy for peaceful purposes. The result was the Treaty on the Non-Proliferation of Nuclear Weapons, also referred to as the Non-Proliferation Treaty, or NPT, which opened for signature on July 1, 1968. By then, 21 countries in Latin America and the Caribbean had already established the world's first nuclear weapons-free zone by signing on to the Treaty of Tlatelolco.

When it came into force on March 5, 1970, the NPT separated between two categories of states: On the one hand, nuclear weapons states – that is, the five countries that were known to possess nuclear weapons at the time when the Treaty was signed (United States, Soviet Union, United Kingdom, France and China). On the other hand, non-nuclear weapons states – that is, all other signatories of the Treaty. According to its provisions, the nuclear weapons states on signing the NPT agree not to release nuclear weapons or in any other way help other states to acquire or build nuclear weapons. At the same time, the non-nuclear weapons states signatories agree not to acquire or develop "nuclear weapons or other nuclear explosive devices." In exchange for this self-denial, the nuclear weapons states promise to move toward a gradual reduction of their arsenals of nuclear weapons with the ultimate goal of complete nuclear disarmament.

The NPT was first signed by the United States, the United Kingdom, the Soviet Union together with 59 other countries. China and France acceded to the Treaty in 1992. In 1996, Ukraine, Belarus and Kazakhstan gave up their nuclear weapons, left over from the Soviet Union when it fell apart in 1991-92, and signed the NPT as non-nuclear weapons states parties. The NPT is now the most widely accepted arms control agreement. As of June 2003, all members of the United Nations except Israel, India, and Pakistan had signed the NPT. However, one signatory, North Korea, had recently threatened to withdraw from the Treaty.

The very first major nuclear arms control agreement was the Limited Test-Ban Treaty of 1963. The LTBT prohibited nuclear explosions in the atmosphere, in outer space, and under water. This treaty was motivated first of all by a desire to reduce and contain the health hazards caused by radioactive fall-out from nuclear explosions in the atmosphere. Due to the fact that many of the radioactive isotopes that were spread around the globe in the wake of such explosions have a lifetime of many tens or hundreds or even thousands of years, the continuation of atmospheric testing was likely to cause additional cancer deaths and other serious health problems on a large scale for many generations to come.

That being said, many countries supported the treaty for yet another reason: non-proliferation. Since it was considered very difficult to develop a reliable nuclear weapons capability without conducting at least one real-life test, a universal ban on testing would also serve as an effective measure against nuclear proliferation. It was probably for the very same reason that most of the threshold states – that is, countries under suspicion of pursuing secret nuclear ambitions – for a long time refused to sign the LTBT.

Also France and China withheld their signature, arguing that the LTBT was unfair since it allowed the technologically more advanced nuclear weapons states to continue testing underground.

Eventually, on October 24, 1996, a Comprehensive Test-Ban Treaty (CTBT) was signed that banned all nuclear explosions, including underground tests, for military as well as peaceful purposes. Both France and China were now ready to sign up. By June 2003, the CTBT had been signed by 167 and ratified by 100 out of altogether 197 countries. Among the countries that had still to sign and/or ratify the treaty were Afghanistan, Cuba, India, Iraq, Iran, Israel, North Korea, Pakistan, Saudi Arabia, Syria, and the United States (United States ratification has so far been stopped by the Senate).

As mentioned, the NPT distinguished between nuclear weapons states and non-nuclear weapons states as parties of the Treaty. However, from the very beginning there was in fact a third category of countries as well, namely, non-nuclear weapons states that for one reason or another had decided not to become parties of the NPT. Some countries, like Cuba, dismissed the NPT as an instrument that served to maintain the existing and, in their opinion, thoroughly unjust world order. Others simply wanted to reserve the option of developing their own nuclear arsenal: either to enhance their regional or international status, to deter military aggression or to underpin their political independence. Not surprisingly, most of the threshold states belonged to this group.

The first country outside the NPT to cross the nuclear threshold was India, which exploded a nuclear device in an atmospheric test in 1974. In 1998, both India and Pakistan conducted several nuclear underground tests, inviting a storm of international protests and some short-lived economic and political sanctions as well.

Meanwhile, the ending of white minority rule in South Africa in 1993 had led to the sensational disclosure that, in the mid-1980s, South Africa had developed and stockpiled a small number of nuclear weapons. The weapons had been dismantled and destroyed in the last years of apartheid because the white government feared that they might some day fall into the hands of militant black opposition groups and be used against the government. Subsequently, South Africa signed both the NPT (1991) and the CTBT (1996) as a non-nuclear weapons state.

Allegations about a secret Israeli nuclear weapons program were frequently heard in the 1960s and 70s. It was not until the mid-1980s, however, that the allegations were backed up with firm proof. In the fall of 1986, a former Israeli nuclear technician, Mordechai Vanunu, disclosed illegally possessed evidence proving that Israel, by all meaningful definitions of the term, was indeed a nuclear weapons state, and a powerful one as well. Drawing on Vanunu's photographs from the bomb factory underneath the small Dimona nuclear reactor, Western experts concluded that Israel at the time probably had acquired enough fissile material to produce more than 100 nuclear bombs and warheads. Today, Israel may possess as much as 150-200 nuclear weapons.

Thus, by June 2003 there were at least three countries – India, Israel, and Pakistan – that were both in possession of nuclear weapons and non-parties to the NPT. In addition, North Korea had announced its intention to withdraw from the NPT. The announcement came after repeated hints by North Korean representatives that their country already possessed a few nuclear weapons.

Alfred Nobel died long before the scientific discoveries took place that would pave the way for the use of nuclear energy for military purposes. In his will, however, he stated that one of the achievements that might qualify someone for being awarded the Nobel Peace Prize is outstanding work "for the abolition or reduction of standing armies and for the holding and promotion of peace congresses". In the nuclear age, the Norwegian Nobel Committee, on several occasions, picked as the most deserving candidate within this category a person or an organization fighting against the spread and build-up of nuclear weapons. Among the Nobel Peace Prize Laureates who received the award, fully or partly, in recognition of their efforts in favor of nuclear disarmament were Philip Noel-Baker (1959), Linus Pauling (1962), Eisaku Sato (1974), Alfonso García Robles and Alva Myrdal (1982), International Physicians for the Prevention of Nuclear War (1985), Mikhail Gorbachev (1990), Joseph Rotblat and the Pugwash Conferences on Science and World Affairs (1995). As long as the risks of nuclear proliferation and nuclear war continue to exist, new Nobel Peace Prizes may well be awarded in this field in the years ahead.

The British professor, politician and diplomat, Philip Noel-Baker, was awarded the 1959 Nobel Peace Prize in acknowledgment of his lifelong endeavor to help refugees of war and to promote arms control and disarmament. Although the award was not given to him primarily for his call for nuclear disarmament, the Chairman of the Norwegian Nobel Committee, Mr. Gunnar Jahn, made several references to this particular aspect of Noel-Baker's work in his presentation speech at the award ceremony. In a recent book, The Arms Race: A Program for World Disarmament from 1958, Noel-Baker had indeed called for an international agreement that could stop the spread and build-up of nuclear weapons. His main conclusion was that even if there were risks involved in every proposed scheme for nuclear disarmament, these risks were not as grave as the risk of doing nothing, pending the establishment of a foolproof control system.

Linus Pauling, a professor and 1954 Nobel Prize Laureate in Chemistry, received the 1962 Nobel Peace Prize for his leading role in the struggle against nuclear testing in the atmosphere. Pauling was not personally involved in the negotiations leading up to the Limited Test-Ban Treaty (LTBT) of 1963 but the Norwegian Nobel Committee argued that the work of Pauling and other scientists had been instrumental in bringing the three main nuclear powers (United States, Soviet Union, and United Kingdom) to the negotiation table. Symbolically, the Committee announced its decision on October 12, 1963, the very day that the LTBT went into effect.

Eisaku Sato, former prime minister of Japan, received the 1974 Nobel Peace Prize mainly in recognition of his opposition to any plans for a Japanese nuclear weapons program and his crucial role in ensuring Japan's signature to the Non-Proliferation Treaty (NPT). In her presentation speech at the award ceremony, Committee chairperson, Aase Lionæs, said that the award to Sato should be seen as "an encouragement to all who work to ensure that the non-proliferation agreement will receive the widest possible support."

In 1982 the Norwegian Nobel Committee decided to give the Peace Prize to Alva Myrdal and Alfonso García Robles, for their important contributions in favor of nuclear arms control and disarmament. In the case of Mrs. Myrdal, a Swedish diplomat, the Committee wanted to celebrate her long and tireless effort in favor of nuclear disarmament in general, and her hard-hitting criticism of the nuclear weapons powers for failing to live up to their commitments under the Non-Proliferation Treaty. Also Mr. Robles, a Mexican diplomat, had a long and distinguished diplomatic career in the field of arms control and disarmament. He was particularly hailed for his crucial contribution to the process that led to the signing of the Treaty of Tlatelolco, which established the world's first self-declared nuclear weapons-free zone in Latin America.

The early 1980s was a period of increasing political and military tensions between the United States, the Soviet Union and their respective allies. By giving the 1985 Nobel Peace Prize to the organization International Physicians for the Prevention of Nuclear War (IPPNW), the Norwegian Nobel Committee wanted to praise an international group of medical doctors that, for many years, had worked hard to spread authoritative information about the catastrophic consequences of nuclear war. The Committee believed that this in turn would help strengthen the growing public opposition to the nuclear arms race that had become so visible in Western countries at the time. In order to demonstrate that the IPPNW's campaign against nuclear weapons was directed against both sides in the Cold War, the Committee asked the organization's two founders and co-presidents, Professor Bernard Lown from the United States and Professor Yevgeny Chazov from the Soviet union, to receive the Prize on behalf of their organization.

In 1990 Mikhail Gorbachev, the last leader of the Soviet Union, was awarded the Nobel Peace Prize "for his leading role in the peace process which today characterizes important parts of the international community". One important aspect of that contribution was the numerous initiatives he had taken in order to stop and reverse the nuclear arms race of the 1980s. As Committee chairperson Gidske Andersson pointed out in her presentation speech at the award ceremony, Gorbachev had been instrumental in bringing about disarmament agreements that were "without parallel in our part of the world, in this or indeed in previous centuries." The most obvious examples were the INF Treaty of 1987, which banned all United States and Soviet intermediate nuclear forces, the CEF Treaty of 1990 on conventional European forces, and the START I Treaty, which committed the United States and the Soviet Union to a 30 percent cut in their overall strategic arsenals.

In 1995, the Norwegian Nobel Committee decided to give that year's Nobel Peace Prize, in two equal parts, to Joseph Rotblat and to the Pugwash Conferences on Science and World Affairs, for their efforts to diminish the part played by nuclear arms in international politics and, in the longer run, to eliminate such arms. Coinciding with the 50-year memorial of the atomic bomb attacks on Hiroshima and Nagasaki, the 1995 award also served as an appeal to the political leaders of the world to collaborate across national and political divides on constructive proposals for reducing the nuclear threat. Founded in 1955, the Pugwash Conferences have brought together scientists and decision-makers with a common desire to see all nuclear weapons destroyed. Joseph Rotblat, a Polish-born nuclear physicist who had worked on the Anglo-American atomic bomb project during the Second World War up until the German surrender, has since then been the most important figure in the Pugwash network.

On October 7, 2005, The Norwegian Nobel Committee announced that the International Atomic Energy Agency (IAEA) and its Director General, Mohamed ElBaradei, were awarded the 2005 Nobel Peace Prize for efforts to prevent nuclear energy from being used for military purposes and to ensure that nuclear energy for peaceful purposes is used in the safest possible way.

At a time when the threat of nuclear arms is again increasing, the Norwegian Nobel Committee wishes to underline that this threat must be met through the broadest possible international cooperation. IAEA controls that nuclear energy is not misused for military purposes, and the Director General has stood out as an unafraid advocate of new measures to strengthen that regime. At a time when disarmament efforts appear deadlocked, when there is a danger that nuclear arms will spread both to states and to terrorist groups, and when nuclear power again appears to be playing an increasingly significant role, IAEA's work is of incalculable importance.

By Olav Njølstad, The Norwegian Nobel Institute.

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