<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Nuclear weapons possess enormous destructive power from nuclear fission or combined fission and fusion reactions . Starting with scientific breakthroughs made during the 1930s, the United States, the United Kingdom and Canada collaborated during World War II in what was called the Manhattan Project to counter the suspected Nazi German atomic bomb project . In August 1945, two fission bombs were dropped on Japan, standing to date as the only use of nuclear weapons in combat . The Soviet Union started development shortly thereafter with their own atomic bomb project, and not long after that both countries developed even more powerful fusion weapons known as "hydrogen bombs". </P> <P> In the first decades of the 20th century, physics was revolutionised with developments in the understanding of the nature of atoms . In 1898, Pierre and Marie Curie discovered that pitchblende, an ore of uranium, contained a substance--which they named radium--that emitted large amounts of radioactivity . Ernest Rutherford and Frederick Soddy identified that atoms were breaking down and turning into different elements . Hopes were raised among scientists and laymen that the elements around us could contain tremendous amounts of unseen energy, waiting to be harnessed . </P>

Where did the idea of the atomic bomb come from