The history of the atomic bomb has essentially occurred in the three stages: the early theoretical research into atomic weapons, leading to the development of the first "A-bombs" in 1945 and their subsequent imitation by the Soviet Union; the development of the hydrogen bomb or thermonuclear bomb, beginning in the 1950s and lasting throughout the Cold War; and the current period of weapons proliferation.
=== Inventing the A-Bomb ===
In the early twentieth century, European and American physicists and chemists made a number of startling developments about the internal makeup of the atom. One of these, by scientists such as Maria Curie and Ernest Rutherford, was radiation: the process by which the internal nucleus of an atom flies apart and sends high-velocity debris (which we measure as radiation) in all directions.
By the 1930s, this knowledge had advanced to the point that chemistry theory suggested it would be possible to create a chain reaction among these destroying atoms, with the particles emitted by one going on to disrupt the nuclei of others. A Hungarian scientist who later provided the impetus for the American Manhattan Project, Leo Szilard, even went so far as to patent this process. When World War II broke out, both the German and American governments hastily assembled research teams to research the possibility of a weapon based on this knowledge. In America, the project was codenamed Manhattan, and was prompted by a letter written by Szilard but signed by a number of other prominent scientists, one of whom was the much more famous Albert Einstein.
Beginning in 1943, large numbers of American, Canadian, and British scientists began to secretly assemble in Los Alamos, New Mexico, under the leadership of Robert Oppenheimer. These scientists, who included such important figures as Enrico Fermi, began to piece together a primitive atomic bomb based on a uranium "gun." Essentially, an explosion would drive two large pieces of highly enriched uranium-235 together at extremely high speeds, so high that atoms would collide, fly apart, and begin a chain reaction emitting massive amounts of energy. (A second design, involving a central sphere of plutonium suddenly compressed by explosions on all sides, was also developed but took longer to be completed.)
It worked in theory, but it took some time for the team to prepare the bomb, using the experimental and (compared to today) somewhat primitive assembly tools of the day. In mid-July 1945, two months after Nazi Germany surrendered, they detonated their test bomb at Alamogordo, New Mexico, in a test codenamed Trinity. The Trinity bomb worked, exploding with the force of a stunning 19 thousand tons of TNT. Oppenheimer, stunned by the power of his creation, quoted the famous words of the Hindu scriptures, "I am become Death, the destroyer of worlds."
The atomic bomb was rushed into production. The first two warheads prepared, referred to colloquially as "Little Boy" and "Fat Man," were dropped on Japan the following month. The cities of Hiroshima and Nagasaki were partially destroyed by the detonations, killing about 200,000 people. The devastation hastened Japan's decision to surrender to U.S. forces, just days later.
That the new atomic bomb would change the world of warfare was obvious to everyone involved - especially to the Soviets. Eager to imitate American success, and aided by a number of spies they had infiltrated into the Manhattan Project (including Julius Rosenberg and Klaus Fuchs), the Soviets detonated their own first atomic bomb, codenamed "First Lightning," in 1949. The age of nuclear warfare had begun.
=== Inventing the H-Bomb ===
The original atomic bombs exploded with the force of tens of thousands of tons of TNT. However, the designers had already set their sights on more powerful designs. Even as the early atomic bombs went into production, Enrico Fermi and another, previously less important participant in the project, Edward Teller, decided that it should be possible to build a far more powerful nuclear bomb based on nuclear fusion rather than nuclear fission. Teller's model would force atoms together rather than blowing them apart.
This process, too, releases huge amounts of energy. The problem was that it required a smaller but still huge amount of energy to start the process going. Teller decided, in fact, that his bomb would need to first set off a traditional atomic explosion, and use the energy from that to power the second stage of the weapon. His new weapon - variously known as the hydrogen bomb, "H" bomb, and thermonuclear bomb - would actually be two atomic bombs in one: first a plutonium fission bomb, and then a hydrogen fusion bomb.
In 1952, Teller's first bomb, "Mike," was blown up on Eniwetok Atoll in the Marshall Islands. The explosion, as predicted, was immense: 10.4 megatons, or 10.4 million tons of TNT - a thousand times more powerful than the original atomic bomb the team had detonated in New Mexico. Mike was much more powerful than expected: the island on which it detonated, Eniwetok, was essentially destroyed. This time, the Soviets were able to replicate the results in just a year, detonating their own hydrogen bomb, "Joe 4," in 1953.
The stage was set for the Cold War. Atomic bombs, while expensive and highly technically complex, could now be manufactured in increasing numbers by both superpowers. In its first years, the thermonuclear bomb increased dramatically in power, with the Soviets detonating a stunning 60-megaton bomb, "Tsar," in 1961. However, as new missile guidance technology allowed more and more accurate delivery systems, the average power of new nuclear weapons began to fall, as it was no longer necessary to use such phenomenally huge explosives in order to reliably destroy targets.
=== Nuclear Proliferation ===
Nevertheless, the power of even one atomic bomb remained horrifically great, in the wrong hands. During the Cold War, the vast majority of nuclear weapons were held by just two countries, the United States and the Soviet Union. The Nuclear Non-Proliferation Treaty even attempted to freeze the status quo by obliging non-nuclear countries to guarantee never to develop nuclear weapons, so long as the nuclear powers remained committed to negotiating eventual nuclear arms control treaties. However, it was obvious that other countries fearing for their own security would eventually attempt to develop their own weapons.
The first generation of the "proliferation" of the atomic bomb, during the 1950s and 1960s, saw the bomb spread to a number of major world powers: Great Britain, France, and Communist China. All of these countries, as well as Israel (which developed its nuclear weapons in secret), remain leading nuclear powers.
However, the second generation was more worrying. During the 1970s and 1980s, Third World countries with sufficient capital to invest began to develop nuclear research projects as well. One of these, South Africa, voluntarily dismantled its nuclear weapons after the end of apartheid. However, India and Pakistan both developed nuclear weapons during this time period, and still maintain nuclear stockpiles, aimed at one another. Nuclear proliferation to these developing countries is worrying because their governments tend to be less stable, they already have a history of conflict with one another, and therefore the risk that nuclear weapons will eventually be used again seems particularly high.
The third wave of nuclear proliferation is much smaller-scale, but also far more worrying. In the past decade, this wave has been led by North Korea and Iran (although Iran continues to deny that it is operating a nuclear weapons research program). These states are probably attempting to develop nuclear weapons to prevent American attacks, but they seem particularly risky because of the likelihood of armed conflict in the future: Iran with Israel and possibly the United States, and North Korea with South Korea and the United States. The even greater risk - that nuclear weapons designs and materials would be shared with terrorists - is particularly disturbing, although fortunately so far it seems that no countries have let control of their weapons slip so severely that terrorists could get their hands on them.