Wells wrote in his book, The World Set Free, that atomic bombs were used in a war between the alliance of England, France and the U.S. against an alliance of Germany and Austria. All of the major cities of the world were destroyed by atomic bombs in this chilling work of fiction set in 1956. .
The fiction of Wells was 24 years ahead of the discovery of fission when Otto Hahn and Fritz Strassman, both German chemists, observed the generation of barium, an element with about one-half the mass and charge of uranium, after uranium was irradiated with slow neutrons. Their former colleague, Lise Meitner, a physicist working in Sweden because of Hitler's oppression of the Jews, and her nephew, Otto Frisch, concluded that the nucleus of uranium had apparently fissioned with a release of about 200 MeV of energy. In comparison, chemical reactions only release about 5 eV per atom. .
In 1942 Enrico Fermi and his team of scientists demonstrated in a Chicago laboratory that the neutrons released by the fissioning of uranium could be used to create a self sustaining chain reaction. In July of 1945 a team of scientists and engineers working under the command of General Groves on the Manhattan Project demonstrated at the Trinity site in New Mexico that a rapid series of chain reactions could be harnessed to make a nuclear weapon. In August of 1945 the U.S. exploded nuclear weapons in Hiroshima and Nagasaki. .
After the end of World War II the Soviet Union developed nuclear weapons and both the U.S. and the Soviet Union identified ways to increase the explosive yield of nuclear weapons by using the fission core (or primary) as a thermal source that stimulated fusion of hydrogen isotopes that would form a secondary yield of the nuclear weapon. During the 1950s multi megaton nuclear warheads were tested above ground. Several of these events were presented on national television so the public had hard evidence of their destructiveness.